building custom exhaust

[Merz]

Im planning on building a custom exhaust and am thinking of attempting to do it myself. I have a welder and pipe bender, but not a lot of experience with either. I am somewhat mechanically inclined. So i guess the question is, is this something i can do?

The system will consist of:

high flow 2 into 1 magnaflow cat
2.5 inch pipe
magnaflow 1 into 2 muffler.

If i cut off the old cat, will i be able to just weld the new one in place? or will i have to bend new pipes from the headers?

The muffler is 2.5 in, 2.25 out. Will i be able to attach the stock tips to the 2.25 inch pipe?

Thanks