I think you are referring to SMBv1/v2 in Windows 10. This has been obsolete for Windws 10 and initially it supports SMBv3+ but anyone can enable the support for v1/v2 in Control Panel > Enable Features.
I am using SMBv1/v2 in Windows 10 with default template and everything works flawlessly. There is no need to change the template unless there is a specific issue that cant be solved otherwise.
Yes I know that. In fact I have used SMBv4 in my router when I was using custom built snapshots but these days I am using stable builds so no more SMBv4.
Yeah samba4 is quite a big package, that's why i also work on getting "cifsd" ready as alternative, but its only in snapshots atm. Still needs some more work before i can setup a PR for 19.x, so look out for it in the next months.