Anyone been through the O-1 visa process without a US employer yet?

Hi everyone! I'm British, working as a digital product designer, and I've been looking seriously at the O-1 visa as a route to work in the US. I have some press coverage and a couple of industry awards, but no US employer lined up yet, so I have a few questions for anyone who has been through it.

1) Did anyone file through an agent as petitioner instead of a direct employer? How did USCIS react to that setup - any extra scrutiny because of it?

2) The advisory opinion: did you get one from a peer group before filing, or did you wait and see if USCIS asked for it? I keep hearing opposite advice on this.

3) How far back did you go with your evidence? I was told to focus on the last 5-10 years of real projects and just mention older work briefly.

4) If you got an RFE, roughly how long between sending the response and a final decision with regular processing?

Trying to plan a realistic timeline rather than the one promised in ads. Any real experience welcome - thanks!