If we are willing to pay fees for an independent mainstream that could support him, would that make any difference, or wouldn’t we be required to if we could prove they could meet his needs?
You shouldn’t have to do this, if no state funded mainstream can meet needs then the LA will have to find somewhere that can, either a specialist or an independent mainstream. But be careful - if you fund a place yourself the LA can argue that you you have made alternative arrangements for their education and this removes their obligation to fund the plan. Very very important to get proper advice on this, from IPSEA or similar.
Bear in mind, my twins places cost nearly £50k a year each, an independent mainstream would be less than half that and even with 1:1 time would still be a lot cheaper. The specialist academy they wanted to name was about £12k a year cheaper, but didn’t include 1:1 whereas our school’s costs did - once we proved 1:1 was needed, our school became the cheaper of the two. It’s all very complex and sounds overwhelming but you’ll learn as you go.
Would recommend joining the Facebook group Educational Equality - lots of parents who’ve been there and who can answer questions.
Non-section 41 schools are a different situation - if you want one to be named the onus is on you to prove that it’s the only school that can meet needs, and the school can’t be named unless they have made a formal offer of a place. I think this is explained on IPSEA, but it’s all quite confusing initially.
If the EP does state that small classes are needed, make sure that this is quantified (small class could mean 25 children as that’s smaller than a state mainstream, or it might mean 5 which would rule out many settings). Once you get your draft plan, go through all the reports and highlight all the needs in one colour and provisions in another and make sure they are all in there. When reports are too vague you can ask the person who wrote them to be more specific - even though the statutory guidance says it must be specific, they will usually refuse or be as vague as they can get away with sadly. But if you can get a private EP report that will give you a lot more evidence.