Salvia is more intense (if you trip hard on it), yes, but it lasts 15 minutes instead of 6 hours. You can probably handle a bad trip on shrooms (you won't jump out a window or anything), but you do not want your first shroom experience to be a bad trip. Bad trips can be worthwhile in retrospect if you've tripped before and know what you're getting into.

Start with somewhere between half an eighth and 2.5g. If you have a grow box, you can usually flip 'em over and get another batch. At any rate, shrooms are a very powerful substance that should be treated with care and respect - don't take too high a dose just because it would be "pointless" to have only a small amount left.

Tripping is more fun in groups. Try and find a friend to split that eighth with, and/or someone who's tripped before to be your watcher. The watcher can either eat some shrooms him/herself (his/her own; you don't have enough for 3 people if you only have an eighth), take salvia while you watch him/her before you trip, or just smoke herb or something for the night. Whatever s/he's on, s/he should be mentally aware enough to be of assistance to you if your trip(s) start going bad.