1. You are buying a car, not an exchange rate. Take a look at a car you fancy buying , calculate the vrt compare the price with the equivalent in the republic.
Shop around on exchange rates though, call the banks and also check transfermate.com
The saving on best exchange rates is decent but not worth buying in itself.
You need to be getting a much higher spec for the same price or a much better price ie a few k saving.
2. cars with a no more than a couple of years on them will generally be easier to sell on. Passats are a very popular import as are various BMW. The 2nd/3rd hand market is good.
3. There is no hassle, try up north, less hassle maybe than a trip to the uk.
Make sure to get an independent mechanic to check the car and get it clear for finance etc. Won't cost much and will afford piece of mind