Thanks a lot to frenchelectrican!
I have stripped my old house to studs. So it's a good time to rewire everything (including upgrade service panel from 30 amp to 200 amp). Yeah, an old house with 30 amp fuse box.
I fired my electrician because I noticed he was fooling around. I will hire another one, but I'd better understand more details by myself this time.
I have two options about the main panel:
option 1: use an outdoor all-in-one box with a meter socket. However, I don't think it's convenient to wire all indoor appliances to the breaker panel.
option 2: use a shutoff switch next to meter. Put three 2/0 + #6 grounding though a 2" conduit to an indoor breaker panel 15 feet away.
I like option 2 more. What do you think?
I have another question:
Is EMT conduit allowed to connect meter, shutoff switch and main breaker panel? I think EMT is very thin and weak (correct me if I am wrong). But IMC conduit is too heavy. I don't know what kind of conduit is allowed (or better suited for my house.)
Thanks a lot!