UKARA membership isn't a licence - it's a way of easily proving a defence for buying an RIF. There are other forms of defence so please try to avoid calling it a 'licence' as it gives people the wrong idea. UKARA is not a government body.
Taiwan Gun are well recommended. They have their own thread in the 'places to buy' subforum - it's always worth searching the website first as your answer is kind of in that thread already: They'll put your UKARA membership number on the outside of the box and Border Force will verify it upon entry, so make sure the address matches up with your registered UKARA one.
So long as you've done that then you'll be completely fine.
As for your second question: Well are the same everywhere so Poland is good too. Again, be sure to make the retailer put your UKARA number on the box. As a side note: I owned a Well L96 and it required a lot of upgrading to get it skirmishable; it's not as common to get parts for this became pretty expensive (had to get a lot of the upgrades from PDI, who are not a cheap manufacturer). If you have a budget and care more about performance than how it looks then perhaps consider a JG BAR as they're more documented and slightly cheaper to buy parts for.
Also, quick answer questions like this have their own thread which tends to get viewed much quicker and also keeps the forum clean if there's no need for discussion: http://www.airsoft-forums.co.uk/index.php/topic/22692-quick-questions-simple-answers/page-39