Depending on how much hair I plan on cutting off, I will cut first then bathe. No reason to bath all that hair that is going to get off, plus having re comb out the tangles.
The face and topknot is totally how you want it to look. I part the hair at the base of the neck on the back to determine what I should leave long (in my case). In my 2, that hair is a different color than the body so it is easy to see.
I have used the clippers both ways depending if I want to get a shorter cut. I take the combs off and use the #40 blade for the belly area. I have watched a couple of dvds and the all said not to touch the bum with the razor. I guess it freaks them out. I will cut the fly away hairs with the razor then scissor more precisely.
Good luck, I was and still get nervous each time (as I was never formally trained, just "on the job training" lol. You'll do just fine.
Post pictures, before and after.