also figuring out a rear end should be a priority. the stock truck rear axle sucks, you can upgrade to a montero for cheap if you use junkyard resources or other options are out there. Im running a ford 8.8", which was also fairly inexpensive but a lot more work to get setup
flux core is great when youre outside in the wind or just need to fix something quick that doesnt have to be pretty. if you hate it at first, just power through it because once you switch to a gas mig youll love it in comparison
km 132 wont hold the power if you want to make 300+. I'm running an r154 on mine with one of Bills adapters, engine mounted with the factory MM mounts. I had to do some custom plumbing with an inline thermostat to avoid hitting the firewall