Wanna go 100% achievements?
Play the game, familiarize yourself with it, get good.
Best is to never spend any gold on permanent upgrades until you beat all four paths.
If you did already, no problem:
Permanent skill upgrades can be reset / refunded.
Permanent character upgrades allegedly (and most likely) do not block the old school achievements.

After you got the old schools, max all permanent upgrades which will give you decent boosts in various ways.

When that is out of the way, make sure you unlocked all skills / weapons, and grab the achievements to beat the game with each pilot as you please.

What might be remaining is the level 75 achievement and the four achievements where you can't get any damage from the bosses.

The level 75 thing is pretty straight forward, you can play path one for example, use the magnet for xp boosting, you can also use the pilot with xp boost and throw in the three difficulty modifiers for additional xp, add the improved data analysis skill for good measure and you should be good.

To beat the bosses without receiving damage, there are different approaches of course, but what worked for me in the end:
Instead of going a full defensive build, you skip the defensive skills that don't help you much at the actual boss fights and simply max damage instead.

I.e. a winning build can be

Weapons:
- Sword
- Autonomous Turret
- Shotgun
- Defensive Drones
- Cluster Rockets

Passives:
- Attack Speed
- Damage
- Critical Hit Chance
- Piercing Projectile
- Boss Hunter

With that you basically skip the Bastion, Rocket Hack, Chrono Shield defensive skills, where some of them could be slightly useful with some bosses...
But you gotta see:
The most effective defense is: High attack speed combined with defensive drones and sword, which takes care of missiles, plasma bullets and enemies approaching from any side, AND, making the boss fight as short as possible.
Other than that you gotta dodge a couple of things and make sure you hit the final bosses with plenty of strikes to end it as fast as possible.
With the suggested build you would usually try to keep some distance, dodge what's coming at you, instantly remove supportive turrets or similar, and whenever possible, go close and place several sword slashes and shotgun hits on top of the damage you're dishing out from distance already.