Heya, according to this episode from this cool podcast if you ever plan on printing (which, unless you're doing some long-scrolly/animated comic, you probably should go forward asuming you will) you should do the following.
- IN GENERAL: You should never work at anything below 300 DPI.
- FOR B&W/LINEWORK: You should work at 600, or even 1200 DPI
- FOR COLOR: You should work at 300 minimum.
(the reasoning behind all of this is explained in the podcast)
When exporting for the web you should do so at the highest quality the site will let you. You might have to check the sites FAQ or otherwise do a quick google search to find out what this is.
From what I know (they may have changed this but I haven't checked) Tapas' maximum size is 940px wide, and any size long, as long as the file size is under like, 2mb or something? In Clip Studio Paint I can set the export dimensions to exactly what they need to be without too much hassle. I usually export as a PNG.
For my comic I work at 11x17' at 350dpi. This gives me a little bit of extra wiggle room when scaling things up/down without having to worry about them being blurry. Ideally I would like to be working at 600dpi, but some of my brushes tend to lag out a bit at that size. That said, some programs are more lightweight than others and can handle larger file sizes better. For example, Paint Tool Sai is EXTREMELY lightweight, and so you can handle very large file sizes on it without a problem, I don't use PTS, but it's got a great reputation. Clip studio paint is a bit chunkier, but when working at 350dpi I hardly ever have problems, this is what I do 99% of my work in. Photoshop is a beast and my computer really has to struggle to use it at 300dpi. I don't usually draw with photoshop, but I like using it for FX work sometimes.
Hope this helps
EDIT: Another note about working at 11x17', is that because of the way standard american paper sizes work, 11x17 sizes down perfect to an 8.5x11 page. This means when I do print I can do so on a big sheet of paper and make some cool large-format books. This is what I did for my Minicomic and people responded really well to my print edition of it. So yahh.