just my opinion, but I wouldn't lose the spare. The rumor is that it may actually absorb quite a bit of abuse in a wreck....at least if it's laying flat other wise...ditch it I guess. As far as the fibre-glass doors. yeah, they're heavy, but you may want to check the laws in your area regarding this conversion. in most places they are illegal for street use, but what they don't know won't hurt ya...I guess.
What year/model car are you driving and what engine are you going with?
This will make a bit of difference in your choices. Let me know.