I wouldn't keep more than 100k in custodial lightning.
Discussion
Ok then it makes sense.
But I suggest you to use Phoenix instead of this Liquid buffer solution. Yes the fees to transact are a bit higher than Liquid tx + Swap fees, but I don't have to deal with liquidity management as you do. I just top up Phoenix every 3 months or so with a big UTXO and then don't have to worry about swapping around funds.
I'm surprised by this since you think having 5M sats on Liquid is ok, which is also custodial.
Liquid isn't custodial. It self custody on a federated chain. That's way different.