Igitur vs Quare

I translated this sentence:

He will, therefore, thank the queen and the whole people.

As:

Quare, reginae et toti populo gratias aget.

Should I have used ‘igitur’ in place of ‘quare’?
Also, since ‘populus’ is plura should it read ‘totis populis’?

Thank you.

Your translation is absolutely right. No modification needed.
Igitur (in the 2nd place) would denote a conclusion, while Quare denotes a follow-up, thus both solutions are probably acceptable.

populus is in the singular, but it denotes a lot of people. TOTIS POPULIS would denote “whole nations”, e.g. all the Romans, all the Greeks and all the Persians…

Thanks for the help.

EL