You can upload it smaller, yes! But it will make the quality a little worse because you're not taking the full space on the app screen - you're gonna be fighting against the white void of that layout.
If you want to do both WT and Tapas, I recommend making it 940px and resizing it to 800px for the former, it's better than sacrificing quality.
The limit for one picture is 2000px times 40 uploads, so 80000px. It might sound limited for you but as a reader AND a creator, it's agonizing to read that much. Any bigger than 60000px is kinda excessive, it's better broken down into multiple parts.