My question involves employment and labor law for the state of:

I am currently an full time employee (receiving W2). I am getting an opportunity to work for another company for full time or part time basis (initially part time and later it could become full time). I work 6:30am to 3pm at my current job.

Questions:
Doing second job is it legal by tax laws and labor laws?
Are tax laws and labor laws same across US or it changes by state... I live in PA..
When I can start my second job (timewise)?
Is it legal to do second job on 1099 ?
Is it legal to do second job on W2 hourly ?

Thanks,
JO