yeah, there is a size limit on photos as well as a limit on the most you can upload in total. to be honest i could probably be a bit more lenient on that since we are still nowhere near the limit of memory use on our hosting. as for how, reduce the image size, the picture you use for your profile is tiny and the limit is ~half a mb. to give context my pic is <17kb. I cant tell you what exactly will work on the image editors that you use but resizing to drop pixel count and convert to jpg and you should be well below the limit. If you click the option to add a pfp it will tell you the size limit you need to get below next to the line saying what file types are accepted.
the site has to pay a hosting service to host the site, there is a total limit of how much stuff (pictures, files, etc) which can be stored. if arocalypse ever bumped up against that limit then it would have to move to a pricier hosting plan (true pretty much wherever you decide to host). In general if you want low cost hosting the cutoff is usually in the low hundreds of gb total. if we got near that we would either have to take a big hike in fees (not sustainable) or mass delete old image content to bring us back down.
as for links, i was unaware of that, could you explain what you mean by a limit of links and where this limit is occuring.
the text is called a signature, you can edit yours by clicking your profile in the top right, clicking account settings and clicking signature on the left menu. I'll add that to the site guide actually, i completely forgot about that.