If i cancel my membership and want to come back later, will my projects still be available? Is it possible to upload a previously exported site?
Your projects will still be available, but you will only be able to edit the # of sites that you are paying for (for free plan it's 1 site). So if you created 10 sites and canceled your subscription you will be able to edit 1 of them (the first one).
Also, there is no way to import previously exported sites because we don't know what you have changed in the code and therefore it would be hard to parse the code.