get a good solicitor and take their advice, if they say go for 60% or 75% then do what they say. Don't back down.
Your ex has proven money is more important than providing for his children, so you need to obtain marital assets to support them. The court will only award what you are entitled to, they won't leave him destitute. Repeat this to yourself regularly.
He will mention you 'taking all his money' being a 'gold digger' etc etc. this tactic is to get you to feel guilty and back down however he is the greedy one not you, 10k from 175k equity! (Get a gold star for every money orientated insult he throws). Pension, savings, shares, vehicles etc are assets too, what about furniture etc. he is so greedy and money focused he is prepared to let his children share one bedroom and have no garden, while he sits with three empty bedrooms - wow. You need to fight for as much as possible, no doubt he thinks driving lessons, uni fees and weddings etc are paid for with dust and unicorn breath. £300 for three kids, great if he is a low earner - check the csa calculator - if not yet another example of his greedy ways.
He may come up with this old chestnut, 'the kids will get the house eventually, when I'm gone' however if he remarries it could mean your kids get no inheritance either, (collect a gold star if he mentions kids inserting the house). Ignore, once again he is demonstrating his greediness - by justifying not supporting his young children.
He has a ltd company, did you receive salary/ dividends? If so you will be a shareholder. You need a very good solicitor ASAp and depending on how much he told you he earns vs what his accounts show you may need this investigating.
Good thing is you aren't living with him. Set up a new email address for yourself, and only communicate via email.
If you worry you are being unreasonable at any point ask yourself one question 'if the shoe was on the other foot, would I live in a 4 bed house and let my children live in a 2 bed with no garden and provide only £300 a month'.