Oh. Haha! Sorry! Yeah 100 grit is finer- Maybe even finer. Remember a belt sander takes off material more quickly than hand sanding. Make long even passes and when you finish use a fine hand sanding with a block to get the joins really smooth and clean!
Get a finer grit that doesn't take off so much material for glue joins. Have a good straight edge to check your surfaces and take your time. You can do it but be patient and keep checking your fit. Use even pressure and don't "park" the sander- if you go too deep on one spot, you have to level the rest to match.
Also- build #1 was a fanned frets 7- check my threads. I've actually got it apart right now tweaking the neck.
My advice would be to either be patient and save for the equipment you need or seek out access to a shop. You will be happy you did and nothing is more frustrating than putting in all this time and effort into a project only to mess something up because you're impatient!
I borrowed a friend's planer for a while to put together some neck blanks but didn't have it for doing finishing on a couple projects. I was using a router and hand plane and I didn't get the results I wanted-too difficult to get that long consistent straight edge. I'm looking at used one's on craigslist. Belt sanding or hand sanding just doesn't give that clean edge either. It's been bugging me. ..