Plugins can have have just one module (there are not many plugins like that, but there’s no requirement for a plugin to start as a multi-module one)
Using an svg file for the panels is not required (you can do all your needed drawing manually in code)
All platforms supported by Rack are 64 bit, so you can make your delay buffers very large (but you obviously shouldn’t go completely crazy with the sizes since you are sharing the memory with Rack and other modules)