Hi,
This is my 1st ever post on this site - hope it's useful....sorry if it isn't.
Personally, I don't think you've asked bad questions with obvious answers - I think they're good questions.
As far as I'm aware, the main differences would be the plug supplied will be a European one rather than an UK one, and the factory default language setting would be set to the country the phone is from - so if you were to consider selling this to fund your next phone (or for any reason for that matter), this could put off potential buyers perhaps?
I was in the EXACT same pickle as yourself, and contacted Samsung UK who confirmed - that if their phone is purchased from a EU member country, the warranty would still be covered by Samsung UK.
In regards to price, it's probably a case of looking around and seeing what's in your budget and are there deals with extras - i.e. seller throws in a wireless charger, dex station egg. And also essentials - such as the warranty, some find essential while others might not care less.
This bit is just guess work on my part (but I'm sure I am not wrong and it's a good guess) but buying from a high street retailer will probably cost more BUT the warranty will begin from day of purchase and you can go directly to the retailer for any probs within the 1st month or so (I think).
BUT if you buy from eBay, FB marketplace or the equivalent, then the price could be much lower and you could find an absoulte bargain, and also have additonal extras such as wireless charger, screen protectors, phone case, etc. The warranty will be shorter as my guess would be it would have begun from the date the seller purchased the phone (assuming they bought it new).
I have never been a fan of forking out loads on monthly contracts which offer the top phone - I fully agree with buying the phone outright and searching for a SIM only deal....but like I said though, that's just my opinion and others may disagree.
I've tried my best in my way ever response - sorry if I waffles on, but I hope it was helpful :)