What do you guys think of the balance of this homebrew I've found. I have already made some changes myself.

Marksman

Preferring to take out your targets at a safe distance you have trained with fanciful new weapons. Your technique is the exemplification of "In quiet, out loud".

Tread softly and carry a big gun.

Bonus Proficiencies

When you choose this archetype at 3rd level, you gain proficiency with tinker's tools, crossbow, heavy and firearms.

Gunsmith

You have learnt how to maintain firearms and craft the ammunition.

• You can craft ammunition yourself using your Tinker’s Tools at half the cost for any firearm you have spent an hour studying.

At your DM's discretion you can also craft upgrades to your firearms from the list below

• Scope (Basic/Superior): Increase the long range factor to 3.5 for basic or 4 for superior instead of 3. (e.g. musket 40/140 or 40/160 )
• Rifled (Basic/Superior): Increase the range bands by 50% for basic or 100% for superior. (e.g. pistol 45/135 or 60/180)
• Technomancy Receiver: Your ranged attacks count as magical for the purposes of overcoming resistances.
• Additional Barrels: You may take one additional attack without the Loading property taking effect. Each barrel requires it's own action to load. Each Additional Barrel add 50% of the base weight to the weapon. The pistol max of 5 Additional Barrels. The musket max of 2 Additional Barrels

Careful Aim

You gain an additional way to use your Sneak Attack; you don’t need advantage on the attack roll to use your Sneak Attack against a creature if you do not move this round, you have no enemies are within 5 feet of you and you don’t have disadvantage on the attack roll. All the other rules for Sneak Attack still apply to you.

Low Profile

Whilst prone

• Your ranged attacks do not suffer disadvantage.
• You gain 1/2 cover against all ranged attacks.

You also negate disadvantage against a target at long range if you hide before you take the attack.

Sniper Nest

After you make a ranged attack whilst hidden and at least 150 feet away from any enemies make a Dexterity Stealth check contested by the enemies group Wisdom Perception, if you win you stay hidden.

Each time you use this feature in a single encounter roll an additional d20 and take the worst result for your Stealth check if you are within 100 feet of any previous location in which you have used this feature.

If you are revealed you cannot use this feature for the remainder of the encounter.

Overwatch

Whilst you have a higher elevation than your enemy

• You have advantage on ranged attacks.
• You may use you reaction to make a ranged attack against any enemy that moves within 5 feet of an ally.
• Your allies do not give the enemy cover.