A few things:
The 900x4000 pixel requirement is per-image but you're allowed to upload up to 40 images/files per episode. So what this means is that you're free to post as much as you want as long as it fits within 40 900x4000 images.
Further, you have the option slice up images that might be taller than 4000 pixels and they'll look seamless in the episode itself! A nifty tool to do that for you regardless of what art software you use is Croppy: https://forums.tapas.io/t/free-image-slicer-croppy-extension/28155
That will take your file regardless of format and make it into files that will upload properly on Tapas (and/or webtoons)! Just give the instructions a read, but it's quite handy!
On the other topic that @AceRagz is talking about, how much you want to include in an update really depends on what kind of schedule you want to try and maintain, how fast you can draw, etc. A lot of hobbyist creators upload ~1 page per week because that's about as much as we can make while still tending to our other responsibilities (work/school/etc) and still maintain a weekly schedule xD But there's nothing wrong with making longer (or shorter!) updates too.
The only thing to consider is that you only get to appear in the "Fresh" section once per day (when you upload your comic you get placed at the top of that list, and then get pushed down as other people upload their comics). That's the main way that new readers can stumble upon your comic, so if you had 2 different episodes you wanted to upload it's beneficial to space them at least a day apart.
Notice I say "episode" and not "page". Again it's up to you if you want each episode to be a single page, or several (or a mixture). There's not really a wrong way to go 
just experiment and see what works for you 
