I live in England and Recently flew From Manchester to Beauvais. I can clear up your transfer issue with regards to getting to Paris.
The best way of getting to Paris, is indeed via the shuttle bus service.
Yes, the shuttle service from Beauvais Airport to Paris (and back) still exists! I doubt they could afford to axe that service given the amount of Ryanair passengers using Beauvais airport as a gateway to Paris...But yes the route is still in action!
It's a direct non-stop journey and get's you to Paris in 1hr15min.
The coaches leave regularly (Roughly every 20mins from early morning til 22.00 at night), all passengers are conveyed. The journey cost is 16euro per person/ per way. You can buy a return ticket from the transfer counter at Beauvais or in porte malliot (Paris) Do note...They is no discount for a return ticket, you just have to pay the price for 2 singles.
When you arrive at Porte Malliot coach terminal in Paris, they is a RER station called Neuilly Porte Malliot within walking distance (The RER is part of the Paris metro, just like the DLR is part of the London underground) To get to this RER station walk to the front of the Palais de congress (Big opera theatre you see from the coach park, google it before you leave so you have an idea of what to look for) then with your back to the entrance of the opera theatre look left; you will see a small pale ''Avis'' car hire building. Head towards it - the RER metro is in that building.
Return Journey from Paris to Beauvias...Don't worry about an early flight, coaches leave Porte Malliot as early as 5.20am and run every 20mins after that. It's a very well run shuttle service to be honest!
Hope that helps, enjoy Paris