APC is not full sin-wave. Look for other options. Most importantly, check the about the servicing available in your local area. Then based on that decide the UPS. Just for 2 fans + 2 tubes 800VA will be a overkill, but its better if you are not planning to upgrade in next 5 yrs. If that's the plan, go for 90AH tubular batteries now and later 4 yrs down the line when battery has to be replaced, go for the 135/150AH. Remember that the battery rating is what will decide your backup time and the UPS rating will decide the capacity.