I think you could spend time encouraging his social skills, this is going to help him get through school because without friendships he is going to have a hard tough time at school.
Encourage him to get involved with all kinds of clubs, sports, cubs, dancing, drama, arts, whatever, but a lot of different variety (obviously not all at once) but group sessions where he has to be with other children.
A truly gifted children can struggle socially so if you can nurture this side from now he will benefit through his life, and especially whilst at school.
The academic knowledge will follow and it will depend on the school as to how much he is encouraged and developed. If he is happy then the academics will be fine.
Labelling your child as Gifted doesnt do him or you any favours and it gets peoples backs up. You know his skills and abilities but other people dont care and you risk alienating yourself if you try and talk to people about this. (Sad but harsh reality). You would need to find children similar to your own before you can have these discussions with other parents.
Also, quite often schools with give a child a G&T label in Year 1 because they can read or can do harder maths but then as they progress through the school the dont have this label any more because of the politics of the school, and then parents get anxious because their child doesnt have the label anymore.
One of my DD was labelled G&T in year 1, but we changed the school and the next school said "so what - what does it matter" (needless to say they havent stretched or accommodated her needs)
|n the early years at school, the social aspect is the most important and the academics follow in later years. It is very easy as a parent to identify your child can do/knows something and you want to extend them and help them improve, but down the line you realise it is not always the best course to have taken. He is only 5 and he needs to lean to have lots of fun and laugh a lot with other kids.