What should I focus on upgrading first in Dead Space?

Specifically, this is a first playthrough on Medium difficulty. I've read that I should try to keep at least one Power Node on me at all times in case I run into a locked door. I am wondering what I should focus on increasing first for survivability: Rig, Stasis Module or my weapons (the only one of which I have is the Plasma Cutter currently).

HP seems like the obvious choice but I'm wondering if upgrading my Stasis Module first will end up preventing me from taking damage in the first place. I'm not sure how often I should be using my Stasis, but it seems like I should learn to use it well pretty early on. An extra 20 points in Energy would give me another shot I presume. I have no reference for how much longer 2 points of Duration will give me though. Is that just straight up 2 seconds? On the other hand, upgrading the Plasma Cutter might also help with the damage prevention. I'm not sure though.

I don't plan on going for the Plasma Cutter only playthrough yet because it's just my first run.

In my experience, the difference between a fully damage upgraded gun and one that isn't fully upgraded is ridiculous. I would absolutely recommend upgrading your plasma cutter first; figure out the path that will get all the damage upgrades in the shortest number of nodes and follow that one. Once you do that, either focus on your rig or figure out what other weapon you like.

I found stasis upgrades to be the least useful; something only to take when you don't know where else to put your nodes. I'd also recommend focusing on only 3 weapons in a single playthrough. Every weapon in the game is fully viable when fully upgraded (except perhaps the flamethrower IMO), so figure out a weapon to upgrade and upgrade it all the way to the end. Trust me, using upgraded weapons makes the game both much easier and much more enjoyable.

Even though you don't want to do a plasma cutter only playthrough right now, the plasma is and will always be a great fall back weapon. Having it upgraded will make life a lot happier in general.

I suggest the rig, though the plasma cutter is your bread-and-butter weapon and makes a great second choice. One great and simple strategy is to alternate between rig and plasma cutter upgrades until both are maxed, then start beefing up the other weapons.

I'd say do yourself a favor: have fun playing with all the weapons on your first run-through, then keep all your upgraded gear for the second run and focus solely on the plasma cutter to get the achievement. It's a great game and kept me entertained for no less than four play-throughs.

The line gun is great for taking down groups of foes, so that's a good choice. The pulse rifle is more useful than you might think; a lot of players rag on it as being useless, but if you use stasis to slow foes you can carve them up at the joints easily with its precise fire--especially when it's upgraded.

Other than that, the force gun was probably my favorite because of the way it pushes them all back and gives some breathing room. When upgraded it's good for most enemies and a total killer for the smaller ones. The contact beam, ripper, and flamethrower are also fun but harder to appreciate in my view.