I was in the same boat as you were not that long ago, after endless research and 4 reseller providers later (over a 2 year period) I finally ended up with a reseller hosting company that provided me with an excellent choice of plans for a good price especially when I've got the exchange rate against me.
mehost.com had my reseller plan started within 10 minutes - I had my name server details, reseller control panel and the reseller web site details in one detailed email.
They also have a reseller panel which incorporates all your personal details, account details, domain name info and a real smart ticket system. Jason the lad with whom I've been dealing with is on the ball and the longest I've had to wait for an email reply or a ticket reply has been 6 hours - and the 6 hours reply was only for a general everyday question that I had about their company. They use WHM & CPanel which is real easy to use and all my customers love it...
With regards to merchant accounts I can't comment as I use the one through my bank with my own accounting software which handles recurring billing. Things to consider - in my experience keep a customer database with info such as the type of account, passwords, database user etctera, do some research on the hosting company, do some research and reading on the server OS and server software, where the servers are located and the type of network, cause customers and potentials always ask these types of questions