I didn't bother registering this last time we moved because online search facilities are now so comprehensive. If you do want to register, you just ring up all of the estate agencies in the area that you're interested in and tell them your requirements. In theory they then let you know when something comes up that you might want. But I just used search sites like rightmove, propertyfinder, etc.
I'll be honest and say that in my experience you'll probably have a hard time getting anything secured, particularly if neither of you is here in person. When I first came here we had to have a rent guarantor even though my husband is British because I had nothing in terms of credit history, etc. In theory it should be a matter of applying for a rental you like (which usually includes giving them a non-refundable fee and a holding deposit), having the checks run, giving them the deposit, doing a walk through ("inventory"), and signing the lease.
I'd probably ask someone over here who one of you knows if they'll ask as a guarantor. Either that or try to rent through a private landlord, but to be honest we just moved and I found it very, very difficult to find rentals that weren't through agencies.
ETA: Most leases are either 6 months or 1 year. I've never seen one for more than that. In my cynical opinion this is purely so the agency can milk you for a fee to renew the lease. I managed to talk ours out of 6 months and agree to a year though, so there might be some flexibility....