Need your advice on Arc'teryx layering please

Greetings,

I'm looking to kit up for some active outdoor winter activities (outdoor skating and XC skiing primarily ... in addition to some sledding with the kids) here in Ottawa where we normally sit between the -5 to -25 degree Celsius range, often with wind.  I'm 6'2 and 185 lbs, reasonably athletic.

After much study, I understand the various Arc'teryx naming conventions but I could use some help determining which products would serve me best.  I was originally thinking of going with a Proton LT Jacket with a Gamma LT Hoodie but I'm rethinking that (Gamma seems redundant). Now, I'm wondering if that would be breathable enough.

What are your thoughts on the following?

Base:    Phase AR Zip

Fleece: Delta LT Jacket

Mid:      Proton LT Hoodie

Shell:    Beta AR (would have to pick up next season most likely due to budgetary constraints)

Questions:

1. How bulky is the Delta LT ... it doesn't look like an athletic fit?  I'd be looking to use it between a base and mid layer for colder days (i.e. -20 or lower).

2. With the base, Fleece and Mid listed above, think I could manage on - 20 to -25 C days on the XC trail and Rideau Canal skating?  Or would a shell be absolutely necessary to keep from freezing?

3. Any other advice you would offer?

Many thanks in advance!

J