BTM is the most fun ride in the whole park, you have to try it. Just know that to get to the island it goes through a tunnel, at the very start, it's quite fast and totally darkl. It's not scary, but I've seen with friends that it helps them when they know its coming. It can also be a bit loud, but you'll find that the tacatacataca noise of the tracks is one of the best noises in the world

The Tower of Terror used to really scare me, I used to look at it and think never in a million years will I go up there. But I finally decided I had to see what the fuss was all about. When we went there was very little queue so I didn't have too much time to stress about it, and I was so busy admiring the perfect theming that I forgot to get scared. Honestly, there is no better theming in any ride in the parks. And then the ride itself, well it's different to anything else. I found myself laughing when I thought I would have been terrified. It's very exhilarating! You should definitely try it - and then get yourself a cool present from the TOT shop to remember it

As for the other coasters, if you find that you totally fall in love with BTM and realise that coasters are not as bad as you feared (I used to be terrified of all coasters, I confess), you can try the others. Start with Indiana Jones. If you're OK with that one and the loop, go for RnRC. Yes, I know it's faster than Space Mountain, but it's a very smooth ride. And the worst is at the very beginning, when they launch you at full speed (I now totally love that bit, by the way). Space Mountain is beautiful inside (if you are able to keep your eyes open, I didn't for quite some time), but it can be a very rough ride, and I don't think they're changing that with the current refurb.
Personally I'm not a fan of Crush because of the spinning, and the queues are always so long that we never really bother with it.
Let us know how you do!!