Generators can be good for off-grid power, particularly if its not needed 24/7, here’s a few pointers!
Assuming all your electrical kit is single phase. You first need to add up the Watts of all the items that could be on at the same time to find your maximum demand. This determines the rating required and the generator must be able to provide this as ‘prime’ power (not standby power which is usually a higher rating but the gen can only support it for a short time).
Give yourselves some leeway, as never good to run at 100%, so go for a generator that has at least 20% spare capacity.
Hopefully you will only be switching light loads but if you have any heaters, you can find when switching on they cause smaller generators to ‘dip’ quite badly (sometimes ‘dropping out’ your technical kit). If any heavier loads you should always switch these on first allowing the genny to stabilise before switching on the tech items. You may also need to oversize the genny a bit more to help compensate for this.
Another thing to think about is run-time, most generators have an on-board tank (often called a day tank) and from its tech specs you should see its ltr/hr usage at a percentage loading i.e. 5ltr/hr @ 75%. A quick calculation will tell you how long this will last between top ups. As you should turn off the generator to refill, suggest a tank large enough to last your whole observing session. Large separate bulk tanks are available for most generators but must comply with regulations so should be installed by a specialist.
Noise and fumes can be an issue so look at the db(A) levels, remembering these are ‘logarithmic’ so a few db’s extra can be quite a lot louder (can always site genny a bit away though or put fence around it as this cuts noise down quite well).
You really should have an earth point in the ground (a stake, mat or something similar) for connecting the generator. onto, I would suggest you get an electrician to help with this as its resistance should be measured. Not usually too difficult unless your area is all concrete! Also use an electrician to wire up your circuits to make sure all complies with current regulations (especially as you will be needing some residual current protection/earth leakage protection).
Hope this helps.