In answer to Question 1, choking would be grinding too fine, to a point where there is no or very little flow from the portafilter.
The double wall filter that comes with most Sunbeam machines has a single hole in the bottom which is meant to produce fake Crema from stale beans.
The single wall filters have many holes in the bottom and rely on you to grind to the right fineness, fill the filter basket with the correct amount of grinds and then tamp with correct pressure. All this comes with trial and error as you learn. I think your filter baskets are probably 51mm internal diameter like the EM3600 and EM3800. Breville BSWF100 single wall filter set fits most of the budget Sunbeam machines with 51mm filters. Single Wall Filter Set | Breville
In answer to Question 2, most here would probably agree that freshly roasted beans from a local roaster or BeanBay (see tabs at top of page), best used within 3 weeks of roasting, is the way to go. Not sure about nitrogen sealed bags. The 3 common rules are brew rate of 60ml in 30 seconds(2 cup filter basket), grind and brew within 3 minutes preferably, use fresh beans within 3 weeks of roasting for best results.
In answer to Question 3, Moisture, Air, Heat and Light all affect the freshness and taste of your beans. Moist beans can also introduce moisture into your grinder and possibly rust your burrs or create blockages. I personally wouldn't recommend keeping in the fridge for this reason alone.
A decent hand grinder may be the way to go initially and can later be used when travelling. The cheaper electric grinders that people seem to start with are the Sunbeam EM0480 or Breville BCG800 Smart Grinder. Check the Grinder section for lots of comments.
Hand grinder thread - http://coffeesnobs.com.au/grinders/2...-grinders.html
Forgot to say, Welcome to CoffeeSnobs! Lots of good info on this site.