Congrats on giving notice. I can't comment on the slow months of microstock since I only have one full month of experience myself. But I did quit my day job just over a year ago, and I know the financial planning can be daunting. If I considered giving notice and really weighed the financial risks, I probably would never have done it. I just needed to make the jump, went for it, and I'm glad I did. Some days it can be tough, but the benefits of not answering to anyone and making your own rules and schedule are well worth it.

One thing I will say about microstock, and self employment in general, is that you should always have multiple sources of income. Obviously you already know this about microstock and upload to multiple sites. Apply the same principle to self employment in general and you won't have to worry about slow times of year. If microstock sales drop off during a particular time of year, you'll have something else ready to fill in the gaps. I do freelance graphic design work, web design, etc. I think most freelancers have a few differnt things going on all at once just to be safe and always have constant invoices going out, money coming in, etc.

Good luck! :-D