Great to hear of a new hostel adventure.
First thing first is of course be very careful setting up in a country that is not your own. I am sure you have taken this in to account but I guess there is a lot that might not be known coming from another country in regards regulations/customs/corruption etc.
I don't really know anything about hostels in Thailand but maybe do a search for some hostels your size/style in Thailand and see if you can find workers/owners on linkedin/Hostelmanagement facebook and get in touch for more info.
It might be good to get a local partner but again this could be tricky as someone being local could take advantage of you.
I guess firstly in regards staff you want to figure out if you are going for 24hr reception.From the size you talk about I would go for 24 hour reception but it will come down to costs. Also will you live on site or not. i would recommend strongly not to as you will burn out. So if you have 24 hour staff you would prob only need one person on reception maybe from 12 to 8. Then figure out busy times during the day where maybe you could assist the receptionist for check outs bookins or make it as seamless as possible. Then you have cleaners. Work out how long each bed rooms takes to clean and by occupancy you should get an idea of hours to clean the hostel at different levels and multiply by hourly wage expected. Dont forget holiday pay and taxes to get your hourly pay out.
Just wondering was it a hostel before? If it was why did it not succeed?