Yeah you got the gist of it. At Sandys it's 20 to the receptionist and 30 to the girl for basic service i.e. OW, sex, massage etc. Extras will depend on the girl you are seeing, but the standard rate seems to be 10 for OWO, 20 for CIM, and 40 for A levels (unsure about this). Most girls seem to adhere to this rate but its best to confirm with them, as they will ask you what extras you're inetrested in before they start anyway.
For Sandys, if you're going for the first time you will have to go there on the day and the receptionist will tell you who is available at what time etc, with pictures of the girls available on the wall. if they are not seeing anyone, the girls will be in the lounge and you can take a look and say hello. After you've decided then you either wait at the lounge for your girl to be done with her current booking or you if she's free the receptionist will call your name and you pay 20 and given a towel, told which room to go to and asked to take a shower.
I persume what might be intimidating for your first visit is the waiting where you'll be sitting next to punters waiting for your name to be called. It's like going to the clinic to see the doctor and punters are the patients basically. It was quite awkward at first but then i just ignore making eye contact with the other guys and perv on the girls instead.
You can also ask for a membership when you are there, all you need to do is give a fake name and they will give you a designated number. This way you can book on the phone and avoid the awkward wait in the lounge for your next visit.
Parlour-wise, I've only been to Sandys so I'm not sure about the others. You can always do a quick search on parlour and agencies on this website like piccadilly selecta, mckenzies, manchester elite etc or just visit the puntingwiki. Hope this helps.