I agree to hold fire on the letter Ohb. He's been trying to rush you all along. You take all the time you need. My instinct when you first posted was to tell him to take a running jump. But, learning about Purple, Frog, and ddrmum's experiences in court I think you do need to play the long game. If you can get a second opinion from another solicitor that may put your mind at rest or make you take a different route.
As for his abuse towards you. Are you still speaking to him on the phone? I assume not, you really don't have to listen to his crap. If it's all texts, can your OH read them before saving and passing them on to the solicitor ? You don't want or need this nastiness in your mind.
As for him saying he won't let DS phone you when he has him overnight. For starters, he doesn't have that, so it's an empty threat. And he doesn't have ds's best interests at heart. The calls are upsetting ds because his dad is a stranger to him - because he chose to sod off for a year. He wouldn't be upset speaking to you (apart from the fact that he'd be missing you) because you've probably spent virtually every day of your life with him. Your ex's logic is non-existent.
I still haven't given twat my new number. Because he's still refusing to sign that bloody form I didn't rush back from my friends (2 minutes drive away). My dd phoned me and said we're waiting outside the house. I said loudly, don't leave daddy drive off and leave you again 
. He didn't, and if he did try to text me afterwards it's floating in the ether somewhere.
Purple I did mention HJM to my friend. She knew him a bit but only through work. She said he was nice, and he seems to know quite a lot of people locally. We got on to other subjects, and it was never the right time to mention it again. General impression was that he was a good bloke though. Sorry you're experiencing a Buttermint tea drought!
Lilac how was the date last night ? Have I missed an update ?