I recommend two connections to power as a minimum, at least one for each oval. With Fastrack, every section can be a power connection, you just need wires with connectors to the tabs under the fastrack sections for that purpose. Lionel sells these wires with connections.
I would set this up as two isolated loops for conventional running as an option. Do this by removing the pins on the center rail between the connecting tracks. Make sure to phase two transformers (CW-80s would work fine) by plugging them both into the same power strip. No problems when trains crossing the connections between the two ovals.
My preference would be to wire two curved tracks, one at each end of an oval; for both ovals (four connections). You might want to isolate some of the spurs, with center rail connected through an on-off switch, so that a conventional loco can be powered down on one of the spurs if needed.
