how the fuck did you beat it on the hardest difficulty with limited saves? I always screw up and save in a bad spot... or die at the damn upside from the train part. =/
Here was my strategy for the first two times I beat it:
Move slowly, and try to keep your weapon drawn as much as possible. Find hallways or walls you can press your back against, and funnel them towards you. Use only the plasma cutter and javelin. After you initially have the option to buy the javelin and get to a bench for the first time, buy as many nodes as you can and hold off on the javelin. I upgraded the plasma cutter's damage to max, but you can upgrade whatever you feel needs it. I never used nodes on additional health or stasis. However, the next time you go to a store buy the javelin. Don't use any of it's ammo at all yet, just collect ammo as you progress. When your inventory has ridiculous amounts of javelin ammo, don't sell it, move it to your inventory. When your plasma cutter has max damage upgrades, then use all of your nodes to upgrade javelin base and alternate damage. Try and save enough money at all times for the next suit, barring an ammo or health crisis. When you get to the Ishimura (chapter 10), you should have enough ammo (and your javelin's damage and alt fire fully upgraded) to use the javelin and only the javelin for the remainder of the game. Most enemies will be one shot, but on black necros and brutes you need to shoot it and then use the alt fire. Don't worry about letting the electrocution animation ride out, switch targets and when you let your next javelin fly the previous one will explode. Fully upgraded javelin rounds into the explosion dismember brutes in one well placed shot into explosion. For the last levels, spend all your money on javelin ammo and a little bit to buy health and sprint past enemies
while still killing them with the javelin. The explosion from the javelin also completely dismembers the regenerator, so he is fairly easy. For the final boss, strafe her and pump javelins and alt fire explosions into her, ignore the little necros. When the marker lets you shoot it, pump javelins and explosion. It will die quickly.
As for the train part, if your damage is upgraded solidly on the plasma cutter you'll be ok. Don't worry about wasting ammo, just hammer out shots.
On xbox, the disc change is a free save. If you die, you automatically go back to the chapter where you had to switch discs. I saved right before the fight in the church of unitology where the leapers are crawling down the wall and boomers ambush you. Then I saved on the level where you have to blow up a fuel tank while an infinite amount of tripods are ambushing you. My last save I used on the final level, just after you fight the regenerator and get away.
As for finding the time, take a nap late in the day. That night, when no one can bother you, just straight up play the game from like 8pm till you beat it. Get some food, drank, and in a party with your bros and you'll have a pretty good time
I know I did
Hope this helps.