A two wire branch circuit is ONE 120 volt circuit or ONE 240 volt circuit. A 120 volt multiwire branch circuit is a 3-wire circuit, and a 120/240 circuit (dryer, range) is a 4-wire circuit.
30 amp services normally serve things like remote signs, remote pumps, remote transmitters, billboards, school crossing signals, and small apartments in a multiple occupancy building. A single family dwelling, in a building by itself, still needs at least a 100 amp service.
Naturally, POCO rules prevail. For instance, all the one's I deal with want the line side of the meter to be served with at least 100 amp sized conductors. This, in my opinion, has more to do with the sizes of taps and crimps they carry on the line trucks more than anything. You won't be able to terminate #10 copper to the load side of a meter can, so you'll be putting some #3 in the load side meter lugs (or whatever scrap you have handy) and tapping that onto your #10.
Expect strange looks from your inspector.
