[creeper]

if you don't feel like jacking the motor up or grinding the tab off of the block you can just tap the drivers side firewall with a hammer so the flange clears, I installed pacesetters on a friends car and that was the easiest way to get it in, passenger side was no problem

I've read it's a bad idea to use solder on o2 sensor wires on the sensor side, the dissimilar metals can cause voltage issues and give weird readings plus the stainless/chrome/nickel plated whatever they're made out of is pretty much impossible to solder to

both Y pipes I had fit into my magnaflow fine, and my stock Y pipe fit into the magnaflow also, so I would think most Y pipes would fit into the stock catback without any problems

you'll be 100% fine driving it without a tune, just wait a few weeks and take it to a shop. buying hptuners is a good idea for the long run if you feel like making other changes and are willing to do tons of research and reading and learn what you're doing, but for just tuning out codes I think it's overkill. you could just buy a used diablo handheld if that's all you ever want to do with it.