ok, i was able to smb connect to my work mac at work from the iPad, so i know it works. i have not taken home mac to work to see if i can connect there. BUT today at home, i created a new user acct on home mac (late 2011 MBP, 10.13.6), *and i _was_ able to connect* to the new user acct -- strange! i still get a user name or password error connecting to my main acct, and i know it's correct. as a test, i changed my password, rebooted the mac, rebooted the iPad and still it would not connect. BUT, i can connect to the new user acct.
at some point, in sys prefs, iCloud was asking me to re-enter my password, both iTunes and MBP ones. i guess maybe because i'd changed my MBP password, and i got excited, thinking maybe all along the iCloud request was waiting on me to re-enter it (that happens every now and then, a request to re-enter it), and maybe that was interfering w/ the iPad smb connecting to home mac.
i also have an old MBP, running 10.7.5, i tried connecting to it, but got a server error. in that system version, there was an option to change my user name in the users and groups section, i do not have that option on the mac i mainly use (late 2011). i have tried variations on my user name, marc.cardwell, or marcc, or marc -- i'm not sure where / how user name gets set.
i looked for some tracerout apps, was confused about which to pick, same for the dummy smb server, so i did not do that. i can connect, but only to the new user acct (guest doesn't work either, oddly).
thanks for sticking through on this, i'll mark it solved and i hope that gives you some credits or points.