I have lone patented on and off for 21 years. Here's my advice:
1 - Set firm boundaries with your ex about everything immediately. Communication, child arrangements, who pays for what when, how etc. I would highly recommend setting up an email just for this and only access it when ready and keep everything.
2 - Try see you and the DC as a team now. Teach them consistently and early to take responsibility for themselves as age appropriate. Share the load as much as possible between everyone.
3 - Be very very very disciplined in how you speak about their paternal family. Just the basics, offer no opinion, stick to facts.
4 - Don't underestimate how much your DC will lift your spirits. It's hard, relentless and overwhelming at times. When it is bring them closer, spend time with them. It really works to think of parenting as your life's work when it becomes a lot. It's a long game.
5 - Always remember that the DC didn't ask to live with parents who live separately. They didn't choose. They feel and see everything even if you think they aren't picking up on it. Mitigate the hell out of this by strengthening and centering your relationship with them. Try not to change too much, too swiftly.
Last but not least, do not use unhealthy crutches if you are struggling post break up e.g. booze or wild nights out or lots of internet dating. Long term you will look back and cringe.
I learnt the hard way unfortunately!