Is It Ever OK to Steal Another Band's Name?
Whether you make money on this tour is up to you. I do think it is very possible, if you can ask for what you need. This is the professional thing to do, as well as the adult lady thing to do. Also, having boundaries and a formalized expectation from the go will preserve your friendship with your friend.
It is standard, if you hire a band or players for a tour, to pay them salary. For a medium-size indie band, that's $500-$700 week. This is someone else's band; they need to assume the risk. Minimum, you should be thinking $50 per show. But don't charge per show, because if there are days off, you are still on the job. A fair base rate, given the popularity of the band, is $350/week, which is $1,400 a month. When you have the conversation with him about the tour, say that is the minimum you need to make. Don't apologize and don't present it like you are sorry you have to ask. Getting paid is not negotiable. This is his thing. You guys are not 22 years old anymore. This is work, this is your livelihood, you are probably having to leave or quit a day job to do this; no mature person should expect you to take a hit for the sake of them furthering their career.
Since the band has a booking agent, it's safe to assume their guarantees are probably in the $150 range. If they are more, if you know they are in the several-hundred-dollar range, ask for more money. If the bandleader balks, be straight with him: This is the cost of doing business. If he can't swing it, walk. Because no one is going to feel good at the end of a tour where they are essentially paying to be able to play on it. Otherwise, he is taking advantage of your friendship -- which is going to make for an un-fun tour and a ruined friendship before you are halfway down the West Coast.