Sometimes it can help to have a small notebook and pen handy just for those times when you're not sure about something. It's easy to forget a query or three when you're starting this game, as there are a lot of things to remember.
One plus though is that with the imminent arrival of 6th Ed you won't have to un-learn 5th Ed too much, perhaps!
Re saving throws: you are always expected to take the best saving throw available to you. This is made clear in the latest Necron FAQ from GW, but applies to all armies in 40k. Invulnerable Saves can always be taken even if the AP is sufficient to defeat your armour save and the weapon ignores cover saves, like a flamer or incinerator, or something like that.
E.