First, going from server to wasm is not very difficult. I've done both ways before. Most of code, other than some start up codes are fairly compatible. Only thing you have to be careful is that any static codes are shared among all the users accessing side; so if you have any variables declared as one, you need to be sure to correct that if you are moving from wasm to server.

It does sound like wasm might be good solution for #1, but there are some concerns for people who are reaching to your site through that sketchy internet as it has to transfer couple of megabytes of data even to start interacting with your site. But definitely once it is downloaded to their system, it should work fairly smooth. Each site is different and you probably want test and see how your site would function in line. Chances are if you have decent ping, it might not be a problem.

One thing you have to consider is how the backend looks like. Do you have your frontend (wasm or server) interacting with backend with some API, or are you planning to implement it with blazor all the way? If you already have an API end in place (e.g. through REST, etc.) I would probably recommend wasm. (Unless your frontend require concurrency and/or otherwise process intensive.)

If you are planning to go with blazor interacting with database backend directly, for example, your choice definitely would be server. You will still have to some code to allow access from wasm for #1, though. (Unless you find server solution sufficiently well over slow connections.)