For what it is worth my 2 cents:
If you can find a way to have a spare phone then get a throw away phone. If not then use your phone with googlevoice but only if you are tech savvy enough to configure google voice well enough not to merge your worlds. When you are not hobbying uninstall voice form your phone, then reinstall when you need to make contact. you can 'text message' from your googlevoice account from a computer.
for all computer work use an anonymizer. TOR works well for example.
# of reviews - no hard rules. The odds of a provider being reviewed and flipped and you getting busted from that are very slim. if there are relatively recent reviews then likely fine. If in doubt PM the reviewers.
No such thing as too many reviews in my opinion - just means lady been around awhile. If you were hiring an attorney, contractor, or doctor you would want someone with the most experience. A lady with a ton of reviews will know what she is doing and you are getting a sure bet in terms of performance, in my opinion. If a high number of reviews makes you nervous due to how many other guys were there - get over it.
I don't give out personal info anymore. Join P411. Myself I see UTR gals and AMP gals - two opposite ends of spectrum.
Highly unlikely an agency dumps your info. They likely keep secure, but they keep it.
To avoid scams stick to reviewed girls. You can't avoid "pimps" for the most part but you don't have to deal with them. most girls have a 'booker' and folks running an agency are pimps in the strict definition. You want to avoid hostile/predatory pimps and sticking to well-reviewed and reputable agencies should help with that.
no set entry fee but in general outcalls range between 250 and 450 based on city. incalls vary slightly less.
more money does not mean better quality once you are above the threshold but it may mean more services. quality is in eye of the beholder.
don't trust anyone else about STDS. protect yourself and stay in your comfort zone. never take anyone's word about how much they test or how clean they are