its a good and challenging project, first of all the synchronization of 2 generators consist of 4 parts:
1- the voltages should be equal in all phases in the 2 generators
2- the 2 generators should be in phase
3- the output of the 2 generators should have same frequency
4- the sequence of different generator phases in the two generators should be the same (meaning if the sequence of phases in generator 1 is :a-b-c, then the sequence of phases in generator 2 should also be:a,b,c)
So you have to make a circuit that do the 4 steps of synchronization.
with respect to the rating of the generator, it depends on the load you have in the building.