newbie questions

Just bought a 98 s/c Riv at auction yesterday a couple of questions....

the belts (both serpentine) seem to be frayed on one side. The s/c beltappears to have been put on the front idler pulley not straight. it reide at a little angle, not all the way in the pulley. I will try to replace both belts this weekend. do I have to remove a motor mount like on my Bonneville 3800?
also what is the reccomended oil weight? I believe in Mobil 1 exclusively

Do I need premium gas? what is the reccomended octane?
the cassette is jammed, and the cd player doesnt work, I knew bout the cassette, but is there a trick to get the cd to play? it loads, but no play...
Thanks in advance,
Norm

you need to take out the bolt in the large mount in front of the engine, place a jack under the engine and lower it down as far as you can, then take the bolt out of the lower part of the same mount, check on my web page, there is some pics of a way to mod. the bolt so it can be changed without lowering the engine, i have the am/fm cd/cass out of my 96 that i would let go for $75