If this is going to be your first venture into Bell TV HD, why not get them to do you the entire Upgrade for FREE. Just call tell them you have an HD receiver, they will book a Tech to come and install all the equipment required, for FREE.

To answer your questions;

An 18" dish is made to look at 1 Sat location, so even if you buy a special part from your FTA dealer it will be a major compromise.

Adding the "Y" bracket from a 20" Dish to your 18" dish will change the focal point of the signals from the Dish surface to the LNBF's most probably resulting in very poor signals.

Yes you MUST skew the Dish to get maximum Signals from BOTH Sat locations. That should be around 98 degrees in the GTA.

Don't waste you money on a cheap Elliptical from the FTA shop. Plenty of true Bell 20" Dish's available on the net, at around $50, you will get the real deal. But why pay, when Bell will do it all for FREE......