first off, good luck, planning a wedding can be a nightmare, and even with a wedding planner, it is up to you to figure out stuff like the date and guest list. the guest was the most difficult thing. we cut from 215ish to 150 after knowing 10 people weren't coming (knowing thier schedules etc as we discussed our wedding date). ended up around 140.
as per your questions
How do you feel about a Friday wedding? Not ideal, some people can't take fridays off, that depends on your guests, with 100 it might not be as big a deal
problem is if you want to spend a last night out with the buddies or do a wedding rehearsal the night before (or both) then people involved may have to take more time off even though they are already in Calgary
unique though
How do you feel about a long weekend wedding?
They suck. we thought about doing a long weekend, and it didn't work out. ended up going to a friends wedding that weekend, and it was beautiful, we could have been camping that weekend, so we were annoyed. its not about your guests, but consider them. also your anniversary will be on the long weekend, which initially seems great, until you realize how expensive travelling anywhere is (and how busy) on long weekends when celebrating your anniversary.
Guest list questions:
When it comes to first cousins, how do you weed them down to the number you want.
your situation is a little more difficult. we basically invited all our cousins from one side of the family each, because we weren't really close with the other sides (my dads and her dads sides). I only invited aunts and uncles from my dads, and only have a few cousins, none of whom are married on my moms side.all or none is probably good, otherwise it shows you are holding a grudge. depends how close you are with the ones you want to invite. I had one my dads side I considered inviting, but wasn't sure if it was appropriate to invite just him, so it was easy to remove him (and his wife) from the list
If a first cousin got married and you werent invited because either A it was rushed due to an "unexpected bun in the oven" or B they are cheap and introverted and only had a justice of the peace marry them with their parents what is your obligation to invite them if you are inviting their siblings who invited you to the wedding? none. it's your wedding, if it is too small to invite them, then that's fine. your situation is tough, but if those cousins which you feel like you should invite are upset, then explain it to them. inviting them but not the others is passive aggressive. invite all or none, IMO
I have about 16 guests that I am not sure will come or not and I would rather not wait until 2 months before I know if they will come or not, are "save-the-date" letters acceptable forms of intial weeding out?
they are totally acceptable, but don't expect much response from those letters. try and be sneaky and find out other ways of finding out if they are going to be busy. the risk of 'save the date' cards is those people actually save the date. if you wait until 3 months before, there is a good chance a few already have plans. and they cost money to send

it depends how much you want those 16 people to be there too!
What would you say are the top 10 highest costs for a wedding?
the reception will likely be the biggest cost. of course i don't know how much it costs to rent a venue in the mountains.
my costs: reception with nice dinner for 140 guests - around $5000 (no alchohol or dj/band/dance)
reception venue $300 (discounted from $800 initially)
officiant: $200
photographer $800 (on the low end but she was fantastic)
wedding venue $300
invitations $60
wedding dress (it may not be your cost yet, but its your future money) around $1000
tux rentals $75 per person
dresses per bridesmaid $200ish each
just to give you an idea
What are some of the questions you would ask the reception location/caterer?
how much per person?
what is their history? (is it solid, any risk of food poisoning)
do they give you anything back if some guests don't show up?
when do you have to give them final numbers for guests?
will they throw in any extras for you?
wheel chair access? if applicable
do they have a backup plan if things go wrong?