Well first thing first is to teach him properly. I totally understand that you want to be his coach/mentor/etc, but if you are really wanting him to get somewhere then you certainly may need to get some help with teaching him especially the basics when the brain is like a sponge and they'll develop habits engraved forever.
Secondly, you need to be firm with a schedule even early on. I mean look at Agassi's early beginnings. His father would MAKE him hit balls for hours on end even if Andre didn't want to, and I'm sure that involved a lot of emotional and physical abuse to keep Andre on the court focused. I'm not saying this is the right way, or to even do this, but if you look at how other pros started out, you'll notice similar beginnings where their parents/coaches really pushed them. It isn't like other sports perhaps where the kid has plenty of time to get disciplined, so you have to start now. However, you definitely have to find out how to make tennis enjoyable for your son. You don't want him growing up to be hating it and then get burned out by his teens. This happens very often.
As for bringing him to a court, who cares how good or what age he is. I took my son out to a tennis court as soon as he was able to crawl (of course I have it easy since I have my parents' old house which has a tennis court in the backyard
) but really, letting him get a feel of the court early on will undeniably make it comfortable for him later on very quickly.
Finally, in regards to his progression, well that is a tough question. We see just even at the pros, there are early learners and late bloomers. Your son will be the same way. Perhaps he'll pick up certain shots really quickly or maybe he'll struggle. You just cannot get frustrated at all with this!
Good luck! My son is almost 3, so we are making some progress too