Carpool stickers in California

Question for those of you in Cali and apologies if this was answered elsewhere, I did try a search. I'm ordering those carpool stickers that most/all electric vehicles have. Not sure if I'll put them on the truck (unsure if they will look horrible), but questions are:

  • If I already have a toll tag, do I have to put that on a cover so it doesn't also get charged when using carpool lanes?

  • With the stickers, does it matter if I'm alone in the car using the carpool lane?

Thanks!