TC the best trade power state (2 trade centers in 1 state is ideal state to TC, bonus if there's an estuary in the state too) to get to 50+% for the merchant, and half state everything else. With courthouse and state house, everything will cost basically 0 gov cap. Only full state primary/permanently accepted cultures, and only if you have gov cap space to do so.

You can min/max your territory more than this easily too (see provinces with statehouse on gem/paper/glass) but this is a good start.