I thought "I'm a great programmer so I'll be a great programmer-consultant". In fact they are two separate sets of skills, and if you don't have the soft skills around consultancy like networking for clients, dealing with payments, and smoothing things over when they occasionally go wrong, you'll need to acquire those skills.

Also get a good accountant. There are lots of terrible accountants. Literally I had one who forgot to file my tax return - you had one job! - and I ended up paying a huge fine for his incompetence then trying to sue him to get it back.