Feats

Changes to Existing 5E Feats
There is a balance problem here some feats allow turning bonus actions into attacks. Polearm Master and Crossbow expert, but not others why?

Polearm Master: can be used with all pole arms and spears when wielded in both hands, but not lances. Can't be used if wielding your weapon in one hand (looking at you quarterstaff)

Healer: + increase WIS or INT by 1

Crossbow Expert: + gain proficiency with all Crossbows.

Durable: + gain Advantage on Death Saving Throws.

Grappler: + increase your STR or DEX score by 1

Charger: You can use a bonus action to Dash. Gain +2 to hit an opponent in melee if you move at least 20" directly towards that opponent. (Because I'm allowing everyone to charge, so original feat is pointless)

Medium Armour Master: + increase your Strength or Dexterity score by 1, to a maximum of 20.

Linguist: + you can learn a new language by studying or being exposed to it. Obviously you start a little rusty, after 1 day you can have simple conversations, 1 month you are fluent, 3 months you can pass for a native speaker. +1 CHA or +1 INT.

Sentinel: The movement of a creature 2 size categories larger is not stopped by a hit from a sentinel

Tavern Brawler: - clarify that the attack to qualify for the grapple attempt can be with any weapon. But you will need to have a free hand (or other suitable appendage) to make a grapple attempt, you can drop your weapon to qualify.

New Feats
Leader: - +1 WIS or CHA. Gain a loyal follower of level 2/3 your own, round up. Talk to the GM if allowed and for specific follower availability. Advice to GM  - recommended for small parties only or it will slow the game down.

Animal Friend: - +1 WIS or CHA. Gain an independent animal friend, or upgrade your familiar or mount to a special. Talk to the GM if allowed and for specific animal availability. Advice to GM  - recommended for small parties only or it will slow the game down.

Thrown Weapon Master:

May drawn and throw, or throw and draw, a light weapon as a bonus action.

+10ft to the range with all thrown weapons.

Your thrown weapon attacks ignore half cover and three-quarters cover.

Being within 5 ft of an opponent does not impose disadvantage on your thrown weapon attacks.

Lancer: If mounted and using a lance or spear, gain an extra weapon damage with your next attack if moving at least 10" before attacking. Only once per turn.

as a bonus action you may direct your mount to knock an opponent prone, or attack an opponent as you pass.

opponents have disadvantage on attacks that react to your movement or that of your mount.

Snap shot:

You don't need to take a full wind up. May use a bonus action to fire a sling at a target within 30ft.

You use specially wieghted ammunition, in your hands a sling does 1d6 damage.

Being within 5 ft of an opponent does not impose disadvantage on your sling attacks.

Poison Expert: The first hit with a weapon that has been previously prepared by applying poison will do an extra 1d8 poison damage. Reapply poison to your weapons with a short rest. GM will need to apply a sane limit to the number of poisoned weapons that can be carried. Recommend 1 melee weapon + proficiency bonus arrow/bolts/or light weapons. GM option to allow stronger poisons at higher levels.

Whip Master: use DEX with athletics to grapple, grapple as a bonus action if you hit this turn, STR with athletics to shove (prone or pull not push) when grappling with the Whip. The Whip is a tool for cool whip-related actions. On a critical hit against a humanoid you have a neck hold. The enemy automatically takes critical damage every round till he breaks out as he suffocates. An enemy grappled by a whip has disavantage to break out unless he uses a slashing weapon

Rapid Fire: When using a bow you may use a bonus action to fire a bow providing you didn't use a bonus action to fire a bow last turn.

Proficiency in all Bows,

Your bow attacks ignore half cover and three-quarters cover.

Being within 5 ft of an opponent does not impose disadvantage on your bow attacks.

Battle Lust: If wielding a heavy weapon and able to move at at least your normal full speed (no heavy armour penalty or difficult terrain), add an extra weapon damage with your next attack if moving at least 10" before attacking. Only once per turn.

Quarterstaff Expert:

When you hit with an oppourtunity attack as well as doing damage you may knock your opponent prone and end their movement.

If you are missed in melee combat by 4 or more, you may use your reaction to make an immediate attempt to knock them prone. Use the normal rules to resolve.

If both hands are holding the quarterstaff you are still considered to have a free hand for grappling purposes.

Outstanding Commander:

Add these benefits to a group of soldiers you normally command, that can see and hear you. (max 200, exclude PCs)

Advantage on endurance, fear and morale checks.

Either +2 to attack with weapons or +2 AC to defense, or +10" move, or +5 to initiative, or some other bonus at the GMs discretion.

Improved Scent

You have a superior sense of smell. You are aware of the location of every being within 30ft. You can attack invisible creatures within reach at no penalty.

You can identify most items and individuals by their scent alone. You have +2 on any skill check where a good sense of smell could help. (GM trip - this sense can be neutralised by strong wind)

Natural Adept

You gain knowledge of any single spell of one of your existing classes of a level you can cast. This permanently increases the number of spells you know and prepare.

Also gain 1 first level spell slot. (thats just a first level slot even if you are a warlock)

Superior Natural Adept

Requires Natural Adept. You gain knowledge of any single spell of one of your existing classes of a level you can cast. This permanently increases the number of spells you know and prepare.

Also gain 1 second level spell slot. (thats just a second level slot even if you are a warlock)

Arcane Sight

Your can see magic, your sight extends into the ethereal plane.

Arcane Strength

Increase your maximum sorcery points by your proficiency bonus.

Item Adept

Prerequisite: ability to cast a 5th level spell.

Gain the ability to attune an additional magic item.

Spells you cast out of items you have attuned are cast at 1 level higher than normal with no extra cost in charges.

Gain a +2 to your Knowledge Arcane skill

Inner Strength

Gain +2 to initiative

Increase your maximum ki points by your proficiency bonus.

Superior Concentration

You can use your magic focus (typically a staff or holy symbol) to maintain concentration on one spell for you. This enables you to use your concentration for something else. If you are required to make a roll to maintain concentration you also have to make a roll for the spell the focus is concentrating on for you.

Requires proficiency in CON saving throws or the War Caster feat

Item Creation Feats
To start to fill out the magic item creation rules I have provided feats to allow certain characters to create magic items. There will obviously be additional costs in terms of knowledge, resources and equipment. This is just a start.

Brew Potions

Scribe Scrolls

Create Wands (for charged and rechargable magic items)

Enchant Weapons and Armour

Create Magic Items (for everything else)

Free Feat: Wizards get Scribe Scrolls at level 3, Druids get Brew Potion at level 3, Clerics get either Brew Potion or Scribe Scroll or Enchant Weapons and Armour at level 3 (whatever the GM deems appropriate for the religion).