Answer's: #1: in my opinion it is well worth replacing rear main seal, especially since you said it has good compression and no smoke, with good oil pressure. This will likely take care of your problem.
#2: Depends on a long or short block. A long block just to drop in and go, stock, somewhere in the $2000.00 - $3000.00 range for a engine from a reliable source.
#3: I would replace my hood mat, helps with noise and insulates the engine a little bit, not much. Where to get them, several magazines have them, but you could check with the store on this site. Look at the top of the post where it says store and push on the button, it will take you to the store page. If you do not see it e-mail them and the owner of the site or someone will get back to you and tell you if they have it or can get it.
Good luck.