I've never purchased a dsm that didn't need some maintenance and repairs done. These cars are getting alot of age on them and a lot of people ignore parts they don't see.
I've removed quite a few dsm engines when I worked for mitsubishi and I always try and leave what I can attached if possible. As stated the power steering and ac both can just be unbolted and laid out of the way. Just watch the lines when you go to pull the engine that they don't get caught or...
Horsepower can very greatly depending on alot of factors including engine health. You can have two cars with the exact setup and both have two different horsepower ratings.
Agree with poster about maintenance and up keep first then mods. Nothing worse then dumping in a bunch of money into upgrades into a car that needs alot of expensive repairs.
I've had good look with hankook tires before and they aren't too badly priced. You can have a great handling car but with junk tires will be worthless. People usually cheapen out on tires and then want great performance and handling which won't happen.
Like others stated the best is to find one that has not been modded but if you have to buy one that has mods try and find one that seems to be built correctly. Too many fast and furious people out there and just want to go fast for cheap. There is no such thing as fast and cheap with still being...
Could be valve seals. Could do a compression test but to really check the health of the engine I would do a leak down test. If you low compression it won't tell you much more then that but a leak down will tell you where the leak is coming from.