OP I’m not sticking up for your ex-husband, nor am I criticising you, however I’m giving you the cold, hard, LEGISLATIVE FACTS. Your solicitor is incorrect in that it is “fine”. As long as your ex doesn’t call CSA to discuss or ask for collection, you will be able to continue as you are doing, however once he no longer agrees or realises he could collect the money (which he is entitled to be paid), at that point you will have to pay (and possibly arrears).
As per my first message you are also defferring 100% of the children’s costs to him (allowances, outings, sports etc) by counting it as Child Support, when these are additional extras (unless agreed) and therefore should be 50/50. As care is 50/50 it would be expected that the children have clothes at both homes, but if you are buying them, his contribution should only be 50% and not the 100% you are claiming.
Why you purchased a property (classed as a lifestyle choice regardless of any circumstances) and how much your mortgage is, is not relevant to your Child Support at all (and CSA won’t care). If your case was CSA collect and you didn’t pay the full amount as you couldn’t after paying your mortgage, CSA would just garnish your wages for the Child Support and you would have to find another way to pay your mortgage.
In regards to him recently receiving a $100k payout, depending on what this money is supposed to be for (ie - unpaid wages from unfair dismissal claim, money to pay medical expenses from an injury etc), YOU may have the right to apply for a Change of Assessment under Reason 8 to possibly have this money considered as income when calculating the amount of Child Support you are required to pay, thus reducing your Child Support Assessment. If the payout was ordered as payment of ongoing treatment from an injury/accident etc, then the income can not be considered.
The assessment is based on income and care levels - CSA don’t care about what’s happened in the background, his mental health issues or why you owe lots of money - this is the assessment, this is what you have to pay.
I would suggest selling the family home ASAP, but be prepared for him to drag it out (and for you to go to court to force the sale).
If he has only received the assessment recently, and from what you say he spends money quickly, be prepared for him to ask CSA to collect to get the money instead.