Here are my observations:
1> Seating capacity is bad as compared to what you would expect. Like, Vitz has more space in the back as compared to Aqua. Also, what I have observed is that the issue is not so much as the legroom, but the seat design and headroom. The seat is raised from the middle, which means that the middle passenger in the back seat will be very uncomfortable, that is, if he is able to somehow get there. I would say that you should consider it more as a 4 seater. 5 people can sit, but you would not like to do that especially on long routes. The leg room for the other two seats is alright. A 5.5 person will be able to sit comfortably, as long as there are 4 people in the car. If you compare it to what you otherwise get in the amount of money you are spending, then you will feel the leg room is lesser.
2> I am easily able to find 0w20 in Lahore city. Oil and Air filters are also available. I haven't had any difficulty finding anything.
3> I used to face issues with ground clearance when 3 or more people seated in the car. I have 185/65R15 installed. So I installed 0.75 inch spacers at the back. Now, the car hasn't touched any speed breaker even with 5 people so far. I don't have any spacers at the front.
4> I would suggest you to familiarize yourself with some basic knowledge of hybrids. Finding good mechanics will be hard. Personally, I have purchased an OBD scanner that works with Dr Prius app/Hybrid Assistant, and also purchased a Chinese knock-off of a Mini-VCI Mangoose cable along with Toyota's Tech Stream software. I haven't had any issues with my Aqua yet, but when I had to diagnose my old first gen Vitz, I first diagnosed the issue myself, read about the possible issues and the solutions, and then took it to someone. I would not like to just blindly trust even Toyota mechanics on the car, as it has some sophisticated tech involved in it. I would recommend heading over to PriusChat website as well, for Aqua/Prius specific information.
As for ceramic coating, I would rather suggest keeping the car regularly waxed instead. A few friends got their cars coated, but maintaining a ceramic coating requires extra care and is expensive as well. Whereas a good wax coat will not cost you much, and will give as good results too.