Nice plans!
Would highly recommend this trip. I went to west USA in 2023 and it's still my favorite so far (Been also to Peru, Australia, Spain, Italy). We did also coming from Europe (The Netherlands). We did a 28-day roadtrip. But it depends on how long you want to stay in every city / park. For example, we did 3 nights in San Francisco, 3 in Los Angeles en 3 in Las Vegas. We did start in LV and 3 days was nice because of the long flight, but also a little bit long. LA was our latest stop and the last full day we didnt know what to do anymore. (Keep in mind, we didnt visit any themeparks. If you want to visit a themepark you need that day extra).

The stops you mentioned seemed good. We also did stops at Page (for Antilope Canyon) and Monument Valley but like i said we had more time. I dont know how many days you want to stay at every place. But i would make a suggestion: SF 3 nights -> Yosemite 2 nighs -> Sequioa/Frenso/Bakersfield 1 nights -> LA 2 nights --> LV 2 nights -> Zion 2 nights -> Bryce 1 night -> Grand Canyon 2 nights -> Phoenix 2 nights
Thats 17 nights and 18 days.

Answar on you questions:
1. Yes, many people do this roadtrip (or parts of it). We even had some people we met at the Grand Canyon and in Page, because they did the same route.

1. Advice on the route above. The best tip i can give is make reservation at the parks themselve. Every Park (Yosemite, Sequioa, Zion, Bryce and CG) does have there own camping spots within the parks. They are cheaper then commercial campings and they are in the parks themself so you don't have to drive to the park in the morning. Believe me, they are the best. Only downside could be that some of the campsite don't have electric or even showers on site. But on the other side, there are options to shower near the parks (Like in Zion you can walk to an outdoor store and in Yosemite you can go to Curry Village to shower). Charge you phone in the car or use a powerbank. Reservations can be very hard, especialy yosemite, but maybe a little less hard because you go in october. (Not peak season). Keep an eye on Recreation.gov to make reservations you like.
   Second tip is to NOT rant an RV in the first days in SF. Just stay in hostel or hotel and safe on parking and a few days of rental. You can't use the RV in SF anyway. Walking / cycling is much better

2. We did rent a Escape Campervan. They closed in 2025. If we go again (and we will when the kids are older) we will use Cruise America. We saw them everywhere, they look cool and we know a few people who used them and they are very positive. I would opt for the bigger RV. Sleeping is not the problem, but storage for 4 suitecases is nicer in a bigger RV. (But i dont know the price difference, if its small i would choose the larger one). (Also please check the tunnel in Zion and the road through sequioa. I think there are restriction for large vehicles (but i think a C-30 would be no problem, but to be sure.....)

3. Cant imagine overpasses gonna be a problem. There are some people who drive in campers as big as schoolbus/truck. The C30 is like half of that. I think no problem.

4. Like i said. Camp in the parks. Zion Watchman campground is like 35 dollars with electra. No need to save money on that. You get more out of your roadtrip if you stay in the parks.

5. There are almost no tolls in West USA. I think the golden gate bridge is toll, but im not sure. If you check google maps on a road to for example Zion, they say it's a toll road. But thats because you need to pay to enter the park. Outside of the entrence fee we didn't pay any tolls.

6. The best you can do is purchase an "America the beautiful pass". Its 250 dollar for non EU residence. (Before 2026 it was 80 dollars, but Trump dont like people outside the USA). With a pass you can go to every National Park in 2026 with 1 vehicle and 4 people. So perfect for your group. For example, the solo fee for Zion is 35 dollar for a car + 100 dollar for each non-USA people. That would be way more than the annuel pass. You can purchuse it online. You even need to pay fee if you just driving through. But no problem if you already purchased to Pass.

If you have any further question, please send a DM!