I have both my guys microchipped and I do believe in it. Both of them are neutered too.
I wouldn't worry too much about weight. Dogs gain too much weight from improper feeding or disease/imbalance.
The most important thing is to choose the right vet. If you look in The YT Library - there are threads there about Anesthesia Protocol (very important for small dogs!) and How to Choose a Vet. Might be helpful for you.