Not sure what I'd advise you, but if it helps for comparison, our son with Aspergers (age 6) and similar needs (though we didn't write down anything for night time) gets low rate care and low rate mobility.
We help him with all the things you have put above, plus some help cutting foods, dressing, and other co-ordination, and he needs extra supervision near roads as he has no sense of traffic or road safety. We also help him with bath time, washing hair and toileting before bed.
We had asked a local charity for their advice before applying for DLA about the care rate of DLA, and they had told us that if it was less than an hour of care per day, it would probably be low rate, if it was more than that, middle rate, and if it was significant night time help (ie you are up several times in the night), then high rate.
In our case, they thought our son should get awarded middle rate, as we estimated we spent quite a lot more than an hour a day; but that we weren't getting up at night to see to him, so therefore he wouldn't get the high rate.
When the forms came back he actually got awarded low rate. We did wonder whether to appeal, but decided not to, as he didn't have a diagnosis at that point (he does now). But this does now mean that I cannot qualify to get carer's allowance - you have to be on middle rate or higher to do that - but I cannot work at the moment, due to DS' needs... so in retrospect, I wish we had appealed.
As your scenario is the other way round, I am not sure what to advise you - is there a local charity or group you could check with, without having to commit yourself to anything? Like you say, even if you think it is quite high, you definitely don't want to loose it altogether.
Sorry. that's probably not much help!