AFAIK hacking won't help you with the modules. In fact it's not as useful as I thought from reading the faqs beforehand. It'll mainly help you with security systems and crates, both highly optional. After first few tries I stopped hacking the terminals and turrets - it's easier to shoot the cameras and the turrets get quickly destroyed by respawning enemies anyways.

No matter what route you go you should invest in hacking. Otherwise you will spend your whole life wondering what kind of treasure awaited you in that locked crate. It will also get you through certain doors and forcefields. As for hacking turrets and cameras, I have played through the game four or five times over the years and this is the first I'm hearing of it. Like seriously I didn't know you could do that. It's easier to just shoot everything. Conserve bullet ammo until you max out Standard Weaps and grab that assault rifle, baby. Especially invest a few modules into Psi as early as possible for the Psi-Pull power and the basic Cryoshot (or whatever it's called). The game is full of hidden supplies that are only accessible with Psi-Pull, and the standard Psi-blast is a great fallback weapon if you ever run out of shells or bullets. With standard weapons you will be swimming in psi-hypos by the end of the game.

There is a huuuuuuge surplus of ammo once you get aboard the Rickenbacker followed by a huuuuuuge drop off once you get to... well, you'll see. You could always just be a weirdo and stick with the wrench, which would be odd considering all the military grade munitions lying around everywhere.

Did wrench only a few times. Hard to do but possible.

On the one hand all those bullets and psi hypos turn into nanite piles thanks to the recycler but on the other you'll spend all that extra on med hypos because you keep dying.

I usually play Psi-Ops with a minor in Hacking (and sometimes a pistol for trash mobs and cameras), and that's probably good enough for a beginner too if you really want to play Psi-Ops. The psi power Cyber-Affinity lets you punch above your weight while hacking, enough to satisfy your curiosity about locked crates and things like that (e.g. occasionally turning off security), anyway :)

The difficulty with Psi-Ops is that the Psi hypos are relatively hard to come by (esp. on Hard), so you have to make every use of your Psi ability count, you can't "spray and pray" because your "ammo" is very scarce.

There's no such thing as "Psi-Ops" in SS2. The psionic military branch is called "OSA", but most players just call it playing "psi".

"OSA", BTW, is never defined!

OSA, without doubt. Why? Because path only determines your starting abilities and doesn't force you to play your "class". So, to be more precise, OSA but played as Marine. ;P Starting as OSA gives you free access to the only "gun" that will never break (although it can still run out of "ammo"): cryokinesis. When you start as OSA every PSI hypo is essentially 20 bullets clip that you can use to shoot at cameras without all that wrenching and jumping hassle. Just start as OSA and forget about psionics for a while and develop hacking/guns/maintenance/other stuff you need.