I got some seeds, a few of them I nicked the wider end where leaf emerges, a few others I soaked in near boiling water in a cup for half an hour. Some produced a clear gel like substance but didn't seem to grow, a couple had leaves emerge but no visible root and one seed had root. I potted them all in potting soil and watered it, wrapping it up in a heating pad to keep them warm.

My main question is, how wet am I suppose to keep the soil? Like should it be soaked? Or just damp, semi-dry? Secondly, was any of that seed prep really required? Couldn't I just sow them as-is and have them grow? I don't think I got a good batch and will try to find another source later.

Thanks for any help in advance.

I handled my Mimosa seeds the same way like most Acacia seeds.
I threw them in near boiling water and soaked for 24h. I then check the seeds if they swell and if they don't I pour near boiling water over the not swollen once again.
The swollen seeds get planted in quite nutrient poor soil mix out of some sand and cultivation soil in a quite big 400ml plastic drinking cups. I keep the soil just moist but not soaked.

Never soaking wet.
Keep the soil moist and the humidity high. You might wanna pull a plastic bag over the plant to achieve this. Once they grown you need to slowly reduce the air moisture so you dont "shock" the plant by suddenly reducing air moisture too much.