Hi, I've come back to this thread after having gotten the merchant account fully set up. Just some advice for all those newbies like I was. Avoid Paypal, their charges are ridiculously high compared with other solutions, in essence the easier it is to get a merchant account the more you'll pay in charges in the longrun. Another downside of Paypal is it takes 5days for the money to come through to you, at a certain amount they will freeze your account meaning your customers can't buy, while they do a money laundering and fraud check on your account. I don't recommend accepting Laser as it is a high fraud risk and even with 3D-secure you are still liable.
We set ourselves up with Ulster Bank and Realex in the end. The rates are pretty good and the Realex system allows you to control how open you want to leave yourself to fraud, I recommend spending a good portion of time learning what each thing does and change the settings to suit before you go live with it. Credit card fraud is a fact and as an online retailer you're a target, especially with a new webshop.