No worries. Bottoming well takes a bit of know how and some practice honestly....
First, I don't have a lot of experience in being a bottom but am getting more and more interested, thus I need some help:
First, how do you prepare to make sure you are clean? I can't see giving myself an enema prior to going since that may arouse questions on the home front. Is it necessary to do that or will a good washing suffice?
Secondly, the few times I did try, I came right away. It was a combination of the feeling and excitement. Once I came I was done. Do you continue taking a pounding after you cum?
Third, any other advice is appreciated.
This topic has been discussed 1,000,001 times...just search the boards for many helpful threads about internal cleansing..
You MUST clean inside with an enema. Nothing spoils a session worse than shitting the bed. Many providers sleep in the room they work in, so if you shit in their bed they have to sleep in it or at the very least, deal with the smell. That's not respectful to the provider. It also makes what could be a great session into a shitty session. (Pun intended)
As for the cumming, it's probably a combination of your prostrate being directly stimulated, and you being turned on by a penis in your butt. I love to cum while being fucked!
As for other advice, perhaps you could get a cheap hotel to do your cleansing before the session....
Thank you, good advice. I honestly didn't consider searching the boards...me bad 
No worries. Bottoming well takes a bit of know how and some practice honestly....
There is a local TS that advertises she has enemas available if you need to clean up when you arrive. She also makes it sounded like a reasonable amount of cleanup time is not counted against you.
It may be wise to play with yourself and get comfortable with anal play it before seeing a provider. That can also be a good test to see if you are sufficiently clean. Would your wife be creeped out if you played with anal toys? If not, playing with toys is certainly a good reason to use an enema and shouldn't draw suspicion.