It worked inside...on a stone floor and on carpet. My grandson wasn't yet able to operate himself, so someone was standing by and guiding. I think outdoor would be ideal - but certainly doable inside depending on your flooring.

It doesn't have a seatbelt but it only has a max speed of 2 mph so you really don't need it.

no

There is no height adjustment for this toy but I am sure he will be okay my son is 2 years and tall for his age and he has a long way to go before he out-grows it. My 6 year old nephew can ride it, it doesn't look too comfortable but he likes it.

No, the height is not adjustable, but your real problem will probably be foot size. The foot space is smaller than a toddler size 7.

No horns or sirens just the sound of the motor running.