I started minding after my own children were at school (because I'm mad). I've been doing it for years and years and I love it.
If you're a childminder and have your own small children, there isn't the same guilt attached to being a working mum as there is if you worked outside the home, with your own children in daycare. However, it does mean that you don't ever have a break from children! I think it's really important to ensure that you get out and about during your working day.
You can get registered but not give up your current job until you had a firm offer of a minding job. It probably isn't going to pay as well, but then you wouldn't be paying out for your own to be in daycare.
I think your house tends to get "well-used" (or trashed!), but as you already have small children, there probably wouldn't be any difference.
You probably won't have to spend much on toys or equipment, you'll probably have lots already. Don't ever buy anything in advance for your minding business unless you're sure you're going to use it.
You would have to pay more for vehicle insurance (if you used car for mindees), public liability insurance isn't drastic. You might have to pay for 1st aid course.
ICP course is definitely not on any more, and its replacement course is certainly not yet available in my area (tutors not trained, manuals not available etc.)