I use guys that are IRATA trained. I don't have all the info as I am not trained myself.
IRATA gives you the training to abseil within an industry environment. Many companies insist on it for insurance, risk assessment purposes. Your rock climbing will stand you good stead as you need a certain amount of hours to progress to each level.
Start at level 1, where you cannot work alone or with another level 1. you have to work along side at least a level 2 as they are trained in rope to rope change over, rescue etc.
level 3 are basically the mountaineers and do any roped access work.
yes you can get work as a level 1 as soon as you pass.
approx £800 to do each level.
better off speaking to someone at the training centre.