OP, I don't say this to be mean; but like alot of the others have said; the word of the day is LEARN. Do all of the reading up on custom recovery partitions, custom ROMs, and Droid modding that you can stand. Just when you think you've read enough, read a little bit more.
And perhaps, you should tell your Mom that you are planning to do something potentially risky with your phone, that way if she says "Fine, go ahead and do it" than you're covered if something goes wrong since you've gotten her permission. Perhaps if she knows what you're doing, she'll add TEC insurance to your line to minimize the cost impact if something DOES go wrong.
I give you alot of credit though, OP. The fact that you've backed off from the modding because you've actually considered what would happen if something went wrong shows you are mature and actually considerate. Alot of kids your age would simply be thinking "Well, if I mess it up i'll just beg Mom until she caves and gets me a new one"