I've started on my plane!!!!

I have a couple of questions that should be easy for you guys to
answer...

The first one is almost stupid but I'm anal about these things: What
grit of sand paper is ideal for sanding/deburring the cuts I've made in
6061-T6? The saw/blade I used really did a good job to the point that
it almost doesn't need sanding but like I said - I'm anal about this
stuff.

The second question is more technical: I'd planned to use 6061-T6 plate
in .125" thickness for my gussets. I've found a source for plate in the
same sizes but in 5052 w/no "-" number listed.
I looked up the numbers and 5052 appears to have very similar strength
to 6061. Can someone advise me if using 5052 is advisable and if I need
to look for a specific "-" number?
The 5052 is only slightly cheaper but much easier to find...I'm
interested in doing the job right.

BTW: Here is where I'm at on the build...

http://68.35.241.46/plane/index.htm