I started brewing in the winter in an apartment where we kept the heat at 58°, so a water bath to help maintain temps and the right yeast strains were all I needed to treat my yeasties right, at least with regard to fermentation temps. One of my first purchases was a CL wine fridge, planned to be used for cool conditioning...it very quickly became used for fermentation temp control which I still use it for!). A kegerator and BiaB AG were next, but I'm not 100% sure which came first.
I was doing 2.5 gallon AG batches, but with the kegerator and kegs, I started doing 5 gallon partial mash + dme batches, eventually going to dual BiaB (2 paint strainer bags, a 16 qt enamel pot and a 20 qt cheap ss pot).
That progression worked very well, and didn't require a lot of expenditures (though when I started kegging, kegs were a lot cheaper), and it seems like a good progression.
So, first: fermentation temp control. Sounds like you've got that handled.
Second: BiaB/Kegging. If you've got the right size brewpot, all you need is a bag to go BiaB, and even the most expensive bag is cheap as far as brewing gear is concerned. Kegging can be expensive, but is completely worth it. Bottling sucks. And if you can get a free/cheap fridge/freezer, it gets a lot cheaper.
That all said, do whatever appeals to you the most first. This is a hobby, so your enjoyment (to the degree that fits in your budget) should be your top priority.