I would suggest you find an installer with plenty of LED experience. The trick with LED's is knowing from experience which products are good quality and which products are compatible with each other. Buying from China via EBay is going to be a lottery..... and one with few winners. Never buy any electrical or lighting products if the seller can't provide a comprehensive data sheet (in coherent English).
Given the lengths and wattages of the tapes you mentioned I'd be looking at 24v tapes, not 12v.