1. Breakers: 20a for the 120v and dual 40a for 240v. Be sure to get the type and style that your service panel accepts. Best to read the brand and "model" off of existing, similar-sized breakers.
2. Room in Service panel for Breakers: If you have enough room, usually that is good. Otherwise two 15a might be replaced with a "twin" 15a breaker, freeing up one slot. Likewise a "twin" 20a could replace two normal-size breakers.
3. Is there sufficient LOAD capacity: This is NOT easy to answer, and apparently not an exact science, somewhat open to individual interpretation, that of the final inspector being most important!
4. Conduit and wire sizes: <I leave that for others.>
5. Safety: Even with power verified (by measurement or test) to be OFF, handle any "connected" wires as if they are ON. The "last" connection is generally to a not-ON breaker, I believe.
See SOC/GID-Meter and CAN-Do Info
2010 Prius, now for sale
2011 LEAF, sold in 2015
2018 Tesla Model 3
2014 Tesla S, Model 3 in 2019
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle