Also, can I keep the 100 amp box to supply the
workshop and office and have a new 200 amp in the new house?

Yes.

--
Regards,
* * * * Doug Miller

Note depending on your existing setup you MAY have to upgrade those
outbuildings, for codse compliance, but 100 AMP should serve them
fine.

If your building a REALLY NICE home you might want to put the main
service underground for appearance sake. Since the main service line
from the road will need replaced anyway for 200 amp service.

I suggest you call your power company and ask them to take a look