First thing first I would not recommend Hostgator as their service has become horrendous - they used to be good. Not anymore. Just my personal opinion from my experience.
As for managing your clients I would say that hosting their websites is not really a good idea because:
1) You automatically take on more responsibility: If one of your clients installs a vulnerable plugin and it gets hacked then all of your other client's websites are in danger as well since it is all shared. Just one example and there are many more.
2) Maintenance becomes a lot harder as the number of clients grows.
3) Most of the time you will have to use your resources sparingly hence you will only be able to provide them with less resources than if they got their own account.
The only good part about this is that as a reseller you can have the subscriptions go to you and if you collect enough clients it can pay off your subscription fee + bring in more money (this being a side business).
I have done this myself and found out that it was a lot of headache especially if you don't have as many clients to get at least a reasonable amount of money back.
As to how to approach them about getting their account set up I would say meet up with them face to face and help them go through the registration process.
If you cannot meet them then do a Skype session and share screens then walk them through.
But the bottom line is that I definitely recommend decoupling your clients from each other and letting them have their own hosting providers.