wanaijua ila bado wamelala.
as long as its a toyota you dont need to worry at all about spare parts.
As for fuel consumption gaia is 2000cc. As far as my experience is concerned with 2000cc cars you will get as high as 8 kms per litre urban trips and about 10 kms per litre for rural trips.
There you have it. I hope it suffices your quench for info.
Yours truly