#1 sounds like there may be an issue with rewrite rules, but I haven’t personally used IIS myself, so I’m not sure what to advise on that, unfortunately.

As for your other two points, though:

#2: I would advise checking out this guide here: https://codex.www.ads-software.com/Login_Trouble

#3: What is the version of PHP that your server is running? If you’re not sure, you can learn more on how to get this information at: https://codex.www.ads-software.com/Finding_Server_Info