Working from home will probably suit you well then MrsB. I can imagine that having to face the workplace when you are feeling low would be awful, whereas with a less face-to-face job you can bury yourself in admin and research on the quieter days.
It can be quite isolating though, so be aware of that and try to make appointments to get out and about for meetings, if only to pay cheques in at the bank or have a coffee break with a friend once a week, so that you don't end up spending a lot of time alone. Particularly if its an online business, the temptation is to stay in your PJs and start work straight away, but it works better if you can treat it like a 'proper' job, get dressed, set hours, separate home & work life, to keep a good balance. Doesn't always work, but you need to aim for that.
With an online business your website and driving people to it (SEO) are the 2 main concerns so do pay a professional to sort that part out for you. Advertising in the traditional sense has rarely paid off for me, I'm sure it must work for some companies, but PR and getting a good name/word of mouth are the best tools, which is great as they can be free!
I have a friend who runs cooking classes for tots and she attends every local fair/fete/event doing demos and chatting to parents while the little ones decorate biscuits etc. She has a slot on the local radio station, is very active on FB and basically throws a lot of her time and effort into her business. It seems to be working well for her as she is always busy, but there's no let-up, every school holiday she is plugging spare places at her classes, she does parties at the weekends etc - its an ongoing slog to keep it ticking along.
Being self-employed is certainly not the easy option, but it can be flexible, which is worth a lot. Could you start it while still in the security of your current job to see how it goes?