I've never heard the word "overtuned" before this past year, yet I've seen it probably 20 times since then.
Anyway, if you get the marine armor and jetdrag, you should do well enough on the torpedo. Get a doctors pouch if you havent already so you can use drugs quickly. With irongut, aegis, morphine, jumping bean, focus stim, you can tank the snakes pretty easily, and you can also heal quickly (antidotes, coagulants, hypos); makes a big difference. I don't know what armor you main, but if you make infused sea wyrm (with dense foam) and infused sea wyrm tabis you'll be immune to acid and very resistant to melee attacks; your jet won't be but at least you can tank more hits. Focus on sea wyrms first in any jet fight. Your choice between the marine armor and the infused sea wyrm armor. Irongut + the tchortist bioscrubber means you are completely immune to all bio damage. Try all that out. Oh, and make sure you're using turbo on the jet.
Vs jets, plasma grenades work very well (strong HEs if you can't make plasma). You'll want to stow away all electrical equipment that you dont use in fights in your jet, because jetters like to throw EMPs (and so should you); then again, with no throwing you'll probably waste these expensive nades and/or hurt yourself. I suggest getting naval jousting and using a spear; you'll do a lot of damage. Maybe against snakes too, actually, especially if you have Hunter. Energy edged would be good against jets but I'd probably go electric anyway.
Save the marsh for when you get the shard. When you do the marsh, use the bioscrubber, infused sea wyrm armor, infused sea wyrm tabis, and bring lots of irongut. If you don't have the scrubber, you can eat canned mushrooms and use aegis instead. Or you could use stealth boosting stuff and try to sneak through it.
Taking versatility and making a good AR and w2c ammo and crit NVGs would make a world of difference and its only one feat, but you don't have to do it.
edit: also you can punch serpents if they are against the shore and you're standing in shallow water