
Do NOT use your melee attack unless absolutely necessary. The game uses checkpoints so deaths are never all that punishing, but it's possible to get yourself into an impossible situation and it's a good idea to have an earlier save to revert to. Save frequently and in different slots. If you run away from Necromorphs or their path to you is blocked, they will find a way into the room you're hiding in. There is no real time limit to any part of the game. If you rush in blindly, you will die a LOT. Make slow, careful progress through the levels. You'll at least break even, so go for it. Nine times out of ten the goodies behind one of those doors are at least worth the price of the node, plus whatever schematics are in there. In most of the chapters you'll find a door that can only be opened by using an upgrade node. Kinesis range is only convenient in a few spots and should be the very last thing you upgrade.
Any time you need stasis to pass an area there will be a stasis recharger nearby. You shouldn't need more than 60 seconds to beat any of these areas, and in the few cases where you do, there are oxygen rechargers all over the place. All of the vacuum sections can be beaten without air upgrades and air canisters (the asteroid section in chapter 4 is tricky but it gives you a timely air canister).
Upgrading air, stasis, and kinesis is a waste until you have nothing else left to upgrade. Upgrade/power node advice: upgrade one weapon first, then the health on your rig and a second weapon, then everything else you'd like. Don't stockpile heaps of med-kits and ammo for a rainy day, sell things off and spend those credits. The difficulty curve of the game doesn't take huge leaps. Even if you don't care about playing the game a second time, Hard is a suitable difficulty for more experienced gamers. Once you beat the game you unlock Impossible difficulty and you can create a save for a New Game Plus, but you can't change the difficulty (and New Game Plus on Easy or Medium is boring as hell). If you are on PC, disable vertical sync! It cuts the frame rate and causes noticeable input lag.