My new tank is ready and the plants just arrived.
Should I start up the Co2 as soon as the plants are planted in their new home? Or, for some reason, should I wait to start it up? If so, for how long?
When I do start it up, (75 gallon) how many bubbles per minute should I use?
Yes you should start it immediately. Start it now if you can. You should shoot for about 30ppm CO2. Use your test kits and the CO2 chart to determine your CO2 saturation. You will probably have to experiment a bit to get it right.