Questions on using an LLC and using it to increase IRA/401(k) conributions

I will be starting a new career in the next couple months and making around 200,000 a year. I currently have a roth IRA. It is my understanding I will be making too much money to contribute to my roth IRA which would mean I need to contribute to a traditional IRA. I am looking to create an LLC mainly for liability reasons but I have been reading more about it being able to be used for contributions to a SEP ira or solo 401(k).

I have a lot of questions and don’t really know where to start so i’ll just list them out:

1. Can I have my employer pay my LLC (and then I pay myself through the LLC)?
2. If I can do this, can I have a SEP ira or solo 401(k) to increase my yearly contributions while also contributing to a traditional or roth ira or company 401(k)?
3. Do you have/know any information on a backdoor roth and if so would I be eligible to use this. My understanding is that you start a traditional IRA and then roll it over/convert it to a roth.

I apologize in advance and will totally understand if anyone responds with “get an accountant or tax guy”. Thanks for reading.