Yeah the idea in principle is excellant, however if you register over seven cars for VRT purposes within 18 months you'll be forced to register to Revenue so they can track your dealings.
Also what you said also clearly constitutes a trade meaning that you would be liable to Irish Income Tax on the profits you make. Regardless of your resdiency. On the up side you could cliam expenses such as all the expenses you mentioned above.
I know of you lad who had a very good system going, he used to buy fairly high end cars from big dealers so they'd still have European warranty, than maybe 4-5 times a year he'd drive his lorry over here packed with cars. Loads of people new him and the goods were genuine so he'd spend a few days over here and sell the lot of them (still with English plates), then the individual would register the car here themselves thus he was avoiding having to register with Revenue. He stopped about a year ago, I think he got himself in some trouble with a few Revenue guys who weren't too happy with him.
You have to remember the car market has fallen apart in ROI now and it's not going to come back over night.
Buy quality cars that are rare over here.