I have been allocated a site in SharePoint Online (latest/greatest version), full privileges to my Site Collection ... and zero privileges outside of that site collection.
I have SharePoint Designer 2013.
Neither InfoPath or PowerApps are options for me.
Q: How can I customize the forms? Simple things: like rearrange the order of some fields; hide other fields?
I looked here, but I don't see any options to visually edit a form using my current versions of either SharePoint Designer or SharePoint. I'm guessing that both have changed since that answer was posted in 2014.
Q: What tools are available to modify a "classic" (.aspx) SharePoint form? Again: InfoPath and PowerApps are not options.
Q: Are there any tutorials you can point me to that tell me enough about SharePoint aspx syntax that I can modify the forms in Notepad? Without a visual designer, SPD 2013 is little better than notepad.