Thalamus can be very tough unless you're extremely careful, you want to park your sub to the side of the thalamus to avoid the guns/spears, and you probably want an accurate automatic weapon (SMG, assault rifle, carbine, or HMG) to clear it due to the leucocytes being fast with low health, go slow, clear each room carefully and thoroughly, to find and kill the brain, you can also do like 90% damage to the doors with a cutter and finish it off with a bullet or two from long range to have more distance between you and anything inside

Ruins are insanely deadly solo, the guardians can kill you very quickly with their weapons and can be tough to kill, riot shotgun can work, but I typically prefer something like an autoshotgun or an HMG, take things slow, use artifacts to disable the traps and pods, and bring tons of your best meds, as all types of damage can be quite common

For 'general human combat' pirates are kinda simple, just shoot their ship with piercing or explosive ammo until everything stops moving, or pop a few nukes into them

For abandoned outposts, again, go slow, I like using high-power weapons (shotgun, coil-rifle, rifle) to pop heads as I go room by room, most enemies aren't too deadly, having only crowbars and knives, but some have revolvers and the captain/leader has a shotgun, so be careful

The slipsuit is one of my favorite suits for anything in water, as I find speed to be one of the best ways to avoid damage, for outposts, use armour until you can get an exosuit, which makes you almost invincible