Google Ads Account email if doing ads for someone else?

Admin question for a newbie please… I’m helping my tech-deficient friend with his website, SEO, and running a Google Ads simple campaign. US here. I want to be able track and administer the Google Ads campaign, but I want the customer(my friend) to use his payment method and also be an admin type user for this campaign. Questions: a) Can my Google Ads account have multiple admins or owners (like a GBP)? If so, Where do I configure this? b) Is there an app or interface for small users other than ads.google site? c) The business I’m working with does mobile car detailing - I think I’ve got the GBP in great shape to account for a no-address business; any tips with Google Ads for this business type?