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If it's only actual Freesat channels, the ones that appear on the EPG, that you're asking about, then it's as glt says, C5HD for pretty definite, and possibly Film4HD.
Other channels come and go all the time though, and the new satellite does add a lot to the capacity for more, so there will probably be many others available "in non-Freesat mode", and some of those may decide to pay to be on the EPG instead.
No (assuming you are in the UK), not if it's already correctly aligned. CH4 HD has been transmiting from 1N for some time and many others have switched to 1N already. It's more powerful so you're unlikely to have any problems.
It seems people in eastern Europe are having problems though due to the tighter footprint in that direction.
In addition to CH4-HD the 5USA and 5* channels (and the plus +1's) recently added to Freesat are from Astra 1N. Before long it's guessed that you will also get a regionalised version of Channel 5 also from 1N.
Your freesat dish now gets channels from 5 satellites before 1N it used 4. Current line up
Eurobird 1 at 28.5E operated by Eutelsat
and nominally at 28.2E operated bt SES Astra
Astra 2A,2B, 2D and 1N. It's called 1N because it's intended for 19E, we are only borrowing it from the Germans till a new Astra2 bird is launched.