Hi Onit, well done for being a strong woman - you sound like you are doing well.
Its sad that the contact arrangements still are proving an issue, it seems like you and your ex have got into the all too familiar power struggle over this. Both of you will rightly so believe what you have proposed is best for your kids (and subsequently yourselves) but a judge / court will be much more impartial.
The court process isn't nice. I don't know how it works in Scotland but in England the courts don't look too favourably on warring ex's who refuse mediation like your ex is. However, as PP have said, the starting point for contact / residency is 50/50 (although 60/40 is usually more likely). Its likely that your ex wold get some mid-week overnights i'm afraid, but from my experience they would take into consideration your concerns and maybe enforce that the mid-weeks don't start until after your sons first term, or that they are phased in some other way.
What are his reasons for not wanting to go to mediation? Sounds harsh to threaten financial support when he is refusing to sort things our through mediation? I'm not sure what financial support he is offering you Onit, but all he is legally expected to pay you is CM, so he is well within his rights to use money as a weapon - if not completely stupid!
It sounds like he is scared - maybe someone (possibly a solictor) is using some scare tactics on him (I have seen this happen, after all, an amicable divorce costs way less than a messy one)!!
Maybe he thinks mediation is a waste as you are both unlikly to be flexible? When my dh was divorcing his exw, things turned really nasty - mainly power struggles that got out of hand on both parts. He spent 2.5k on mediation with her and she still wouldn't budge on her contact terms. In the end he had to take her to court to get an order, costing him another 1.6k