Just reading through this thread and i think the problem here is the OP's expectations. Not unreasonably he wants a response to his enquiry but clubs don't really work that way. The best one can expect is "turn up for the Sunday run" - if you're lucky you'll be told the distance and speed first!!
Cycle clubs, IME, are not especially efficient organisations and unlikely to respond to letters or emails. My current club publishes an events calendar, works really well and is the height of efficiency round here!! All other communication is Facebook or word of mouth.
The word club might be the problem. The three clubs I've been a member of are pretty loose organisations
The way to join a club is turn up at the meet point 15 minutes early. Ask the ride leader if you can tag along, if you like the riders join the club. Most clubs allow newbies 3-5 rides before they must join, the number usually depends on the clubs insurance. Alternatively find out when / where club night is and pop along.
Cycle clubs aren't really exclusive but I can understand to a potential newbie why, looking from the outside, some appear to be.
You 17.5mph will be fine, it will probably move up to 20 in a group!! As fir etiquette, sit in the middle of the group, observe the hand signals and learn them, ask if you don't understand, and keep with the pace.