Welcome to the Lugerforum Hay.
In answer to question 3, the availability of gunsmiths that know what they are doing when it comes to Lugers is very limited.
If you should require service of any kind, I would recommend that you bring the problem to the forum and you will be advised at that time on how to handle it... There are several really good lugersmiths that are members of this forum. Not to mention almost a 1000 folks worldwide who are more than just familiar with the Luger who will be glad to bend you ear with advice
I also recommend buying a Luger that is already mismatched to shoot if that is your objective. If collecting is not your thing, then sell the gun you have to someone to whom all matching numbers is important and then use the cash to buy what fits your needs... On second thought, I can't think of a single valid reason for selling a Luger once you own it...
Just save your money and buy another one.