If you don't know where you're going it's unlikely to be a success. Tumblr is not a good platform for writing; blogs are better and Wattpad has a niche market, but is far and away the best platform for serial fiction. That said, I would advise against it since I've seen that it very rarely works out well unless you're really good at coming up with work on the hoof.

Don't share anything that isn't finished and polished. Readers may be ok with less than stellar work, but to keep an audience engaged, you need to have something that knows where it's going. Critique is better obtained privately or through a website where that's the objective, because you need your audience to keep coming back, and if your work is first draft quality, there's not much gained by it and plenty to lose.

Plus it may turn out that you can't keep up the output and the aspiration of a chapter a week isn't attainable in reality.

Don't share anything you might want to publish with an external publisher (because you need to have excellent numbers to sell it later). It's possible to get deals this way, but not if you're posting draft-quality work that can't sustain an audience's interest. Don't think of yourself as an exception. A publisher may snap you up - there are contests run by Harlequin etc there. But you've got to be good, and completely winging it will stack the deck against you.

IMO finishing a good copy and working on revisions is a good idea. If by then it's clear that you want to publish it, you still have options. You may decide to go ahead and post, and use the time while posting one story to write the next. You may find out you need to work on stuff privately first. You may shop it around agents. Et cetera. But just posting-as-you-go risks a lot more than you gain.