Can this also mean this is my teacher (singular) as in a respectful way?
Yes, it can. But since वे is the plural of वह ('that') rather than यह ('this'), it would be 'That is my teacher'.
Can this also mean These are my teachers?
That would be ये मेरे शिक्षक हैं.
ये is 'these' and वे is 'those'. Both can be used as 'they'.