Start with bomb as your weapon
Beyond that I think most turrets prefer to have multiple weapons having one high-tier weapon for early game. Look at mods and take any that look really good, especially if you can combine 2 mods in a way that they’re doing opposite things to damage or firerate

Modifiers to firerate, damage, and projectile count are addictive/subtractive. It's better to get +80% firerate and +50% damage than two damage mods that add up to 150% damage, for dps. And +projectile are great.

How do you deal with the shooter enemies? The weapons are too slow and inaccurate to deal with them reliably. Again I'm getting increasingly frustrated with this game.

Use semi-accurate weapons. Bomb isn’t too slow to deal with them, and if you turn it into dumbfire or bazooka it’s still good for early shooting enemies. Don’t let them pile up.

what about when 2-3 basic ones appear with a couple of higher tier ones. That ended my last run because I couldn't hit them with what I had.

Kill them quickly before the others start shooting, and try to avoid filling your weapon slots with stuff that’s too inaccurate to hit them

Flamethrowers are also great against shooters

How do I make a flamethrower?

AAG is the regular one, then AAAG is much bigger shots whereas AACG has more range essentially

hmmm ok. ill try that out.

Yeah you only need to hit with one projectile and the shooty guy dies of burn

what about the 5 red bubble chargers? The ones that ZOOM towards you in about 2 seconds?

Either fast reaction time (they will usually go down almost instantly if you attack them) or a weapon that covers a large area around you (GGGG is a favorite for this, but some other weapons can also do well with sticky or speed down)

Sticky will be your best friend. The Ramming microbes will just crash into the lingering projectiles and take care of themselves if you can maintain a ring around yourself. AATT Homing mines might help too even though they do not stay in one place. Lasers such as CCCC or AACC (And if you add sticky, CCCT as well) tend to also be good against them (Along with obliterating erratically moving enemies). If that does not quite work, ACT, ACTT, or ACCT could help due to their proximity detonation making it much easier to hit targets. Just don't try to mix sticky with Proximity because unless you add several size upgrades, it will just become a highly inefficient Improvised mine.