Something I've had an issue for years with in 5E is just how WEAK Martials are and how Heavy armor never feels worth using. When you use light armor have high dex and a shield you have the same AC as full plate and a shield which makes 0 sense logically as it is. Not only all of this but Martials just feel super weak over all in mid to late game.

I've tried experimenting with adding 2 resistances to heavy armor and 1 to mediums and it seems to help but alone it isn't enough. So my group and I tested new shield rules where shields have a bash as a Bonus action and different AC addition based on type for example a Buckler only gives 1 to AC but doesn't require prof to use. A Round and Kite give +2 as standard and do require prof but have the bash and Great/Tower have +3 and can be planted as a bonus action to provide half cover to allies. These changes my group loves and they add more tactics and customization to these gears over all.

But I cannot help but feel while these vastly improve, they either do to much together or not enough alone and would like suggestions on ways to better improve the system. Especially with ONEDND coming up fast and its looking like Wizards have 0 plans to fix the system themselves.

Well your Buckler is just a straight boon to non-martials, giving wizards, sorcerers, bards, rogues, warlocks a free +1 AC. Bonus action bash is already in the rules from Shield Master, you may as well just give them that feat for free, this would give them nice defense against spells and AOE that martials are typically lacking as well. Resistance in 5e is extremely powerful, you'd be better off just giving them the Heavy Armour Master feat for free instead. But the problem you'll find is that neither of these scale, so they will make martials extremely powerful in the early game and just push back where you consider martials "weak" a few levels in late game.

The advantage of Heavy Armour is that it lets you focus on Strength and strength weapons deal more damage than dexerity based weapons - mainly because of feats - Polearm Master + Great Weapon Master makes heavy weapons much more powerful than light / dexterity based weapons. In addition, grappling is very good as battlefield control and likewise requires investment in strength. So like with Shield Master and Heavy Armour Master, you could simply give your players Polearm Master and Great Weapon Master feats for free if you want to buff martials even more.

In a similar vein, Strength has only a single skill associated with it but that skill covers many more situations than any other skill - Athletics lets you open chests, locked doors, blocked / collapsed tunnels, swim against a current, climb a tree/wall/cliff, immobilize a fleeing creature, jump across dangerous terrain, etc... So you might want to give all martials Expertise in Athletics to ensure no other character can rival them. 

Since your group likes tactics and customization, you might want to borrow some weapon properties from Pathfinder: e.g. give each weapon one or two of the following and only allow martial characters to use those special properties:

• Grapple : when you hit a creature with an attack with this weapon, you can choose to grapple the target rather than deal damage to them.  - requires: deals Piercing or Slashing damage
• Shove : when you hit a creature with an attack with this weapon, you can choose to push the target 15 ft away from you rather than deal damage to them. - requires: Heavy Weapon
• Trip : when you hit a creature with an attack with this weapon, you can choose to knock the target prone rather than deal damage to them.
• Backstabber : when you roll an attack with this weapon with advantage, it deals +2 extra damage on a hit. - requires: Finesse Weapon
• Deadly : when you roll a critical hit with this weapon, it deals 1d10 extra damage.
• Sweep : When you make an attack with this weapon held in two hands, if you miss with the attack with this weapon, you can make a new attack against a different creature that is also within your reach, you can use this features only once per turn. - requires: Two-Handed or Versatile weapon that deals Slashing or Bludgeoning damage
• Parry : when you are targeted by a melee weapon attack, you can use your reaction to attempt to deflect the blow using this weapon, you gain a bonus to your AC equal to your proficiency bonus against the triggering attack.
• Twin : when you are holding two of these weapons, one in each hand, you gain a +1 bonus to damage with each weapon. - requires: One-Handed Light weapon
• Tethered : the weapon is attached to you by a tether, when thrown a distance within the first range increment of the weapon you can retrieve it as a free action using the tether.  - requires: Thrown weapon
• Vault : you can plant this weapon in the ground when you jump to increase the distance you travel by 5 ft (10ft if the weapon has the Reach property) either vertically or horizontally. - requires: Polearm
• Climb : you can use this weapon to assist in climbing, and to fight while climbing, it counts as a Climber's Kit for the purposes of climbing, and you can attack with this weapon while climbing - requires: One-Handed / Versatile & deals Piercing damage
• Armour Breaker : when you attack a creature wearing armour or holding a shield, and the attack misses but would have hit if the target was not wearing armour/shield you reduce the AC of the target by 1. - requires: deals Bludgeoning damage
• Momentum : when you hit the same creature multiple times in a row, on the same turn, each subsequent attack gains +2 bonus to it's damage (e.g. hitting a creature twice in a row the second attack gains +2 damage, hitting it three times the third attack gains +4 damage etc...) - Cannot be a Light weapon
• Brace : when wielding this weapon, you can use a bonus action to enter a defensive stance until the start of your next turn. While in this stance you have advantage on opportunity attacks made with this weapon - requires: melee weapon without the thrown property.

I like damage reduction for heavy armor. Something like the Heavy Armor Master feat should just be intrinsic to heavy armor, but it should scaling value. Maybe proficiency bonus? That's pretty strong, but it still wouldn't make heavy armor an autopick. Of course there are niche builds that already perform very well in heavy armor, and they don't really need the buff. Maybe this would need to require a shield as well.

But as noted above Heavy armor is interconnected the lack of benefits of a high Strength score. Making that more worthwhile can also make heavy armor more worthwhile, although it won't change the feel that plate mail is no more protective than half plate.

I'd agree on just about everything you suggested except bash being shield master. It isn't in the shield master description at all and shield master is such a strong feat no way should anyone get it for free.

I've never played pathfinder but I'll certainly give these a try