Auto Trans Advice

[Vegas Mach1]

Well as my Machs are getting on in age (90k and 80k), Both are starting to have their auto trans slip a little. I want to do a fuild/filter change. Can I do this as a DYI in my garage? I thought about using a pump to suck the fluid out as much as I can, then take off the cover and replace the filter & gasket. Does this sound reasonable? Or just take it to a shop as it can be quite messy and I most likely can't get all the fluid out?
Also towards the rear of the trany by the drive shaft connection there is a bolt and a plastic piece. I seem to have a leak right there, I think I over-tighten the bolt. Ford should carry this part, right?
Recomendations on the best trans fluid to use would be appreciated.

I've been really lucky to this point with both of my Machs little or no issues, so now I get to play mechanic.
TIA