I can't say on the second part of your question, but with masturbation you learn your 'hot spots', which might not be stimulated during sexual intercourse. If you get too used to masturbation you won't be able to get off during sex. My advice would be to stop masturbating altogether. When you have sex, let your girlfriend perform oral sometimes. That might help you to wean yourself off masturbation and help you to become stimulated enough to ejaculate during sex.
You can get circumsised but that may hurt, maybe before you go to this extreme try Beargizmos advice first.
First thing I'd try is keep your hands off the thing for a couple weeks..before you try intercourse again..it gets used to the feeling of your hand and when presented with a lubricated vagina doesn't know how to react...
I'm sorry I can't comment on the other parts of your question
Jim