Approximately 4-6 megapixels for 35mm film, and 12-20 megapixels for 120 6x6 film, if you have a phone that supports RAW capture and that has at least a 12-megapixel camera. Phones without RAW support, or with less sensor resolution, will have smaller output files.
FilmLab processes the raw data it receives as input - if it didn't do any processing, you'd just get an uncropped picture of your negative or slide. So there won't be a truly raw output option. But FilmLab will offer the ability to save output in lossless formats. These will include 16-bit TIFF, and probably Linear DNG.
I'm still learning about the different options, so I can't give a definitive answer to this yet. By I can tell you about my personal experience so far.
I currently own two light boxes, both of the slim LED variety. First is a Huion A4 table which I bought on eBay. It works well, except that the power supply that came with it caused some flickering (I swapped it out for another standard USB power supply), and it has a slightly cold color cast.
I also have an Kaiser slimline plano light table, which is smaller and more portable, has a built-in battery, and a warmer color. It's advertised as being full-spectrum, which could possibly give more accurate colors, but I haven't tested that yet. You can find these online at B&H, or many retail stores. At $118, it costs probably 2-3 times as much as one of the cheaper light tables. (Disclaimer: this table was sent it to me for free by the US distributor when then they heard about FilmLab).
I will try to add more specific information about light tables before the FilmLab beta is released, so backers can have a chance to order a good light table ahead of time.
If you just want to view your negatives, a tablet makes a perfectly fine light box. But if you capture scans of film on top of a tablet screen, you'll be able to see the RGB pixel grid shining through your film. I'm hopeful that someone will experiment and find a good, easy-to-find diffuser material that can be placed over a tablet screen and even out the light. But for now, for best results I recommend a light box.
Yes, FilmLab will support all film aspect ratios! It's possible that it will have trouble with some of the more obscure ones at first, but by the end of the beta period any aspect-ratio-specific bugs should be straightened out.
For image formats smaller than 35mm half frame, you would need some kind of close-up adapter to let your smartphone camera capture enough detail to be useful (see the following FAQ). Without a closeup adapter, you could still use FilmLab to preview very small negatives, but they will be noisy, and captured scans will be very low resolution.
I've experimented with a couple of add-on macro lens on my iPhone, and found that they actually had too much magnification for 35mm: I couldn't fit a whole 35mm frame in the picture and keep it in focus. The cheaper lens I tried also introduced a lot of distortion and vignetting.
That said, FilmLab isn't tied to any particular magnification, so if you can find a lens adapter that works for your phone and for the film size you're capturing, there's no reason why it shouldn't work.
Don't see the answer to your question? Ask the project creator directly.