I had a 7300, I'm surprised your 7100 weighs what you say, I was sure they're in the 30-35 pound range, quite curious how you weighed your ride.
The FX bikes as I recall have 700x32 tires compared to the 38s on your 7100. I find that the thinner tires seem a bit 'squirrly' after riding 38s for quite awhile, but I still prefer the 32s overall.
Personally, I just don't see the need for disc brakes on a commuter ride, some on these boards are sure to disagree, but my v brakes are proven to be powereful enough to lift my back wheel off the ground. Discs do take less effort to use so if you had issues with stopping on your 7100, then maybe discs might be a good idea. If braking hasn't been an issue for you, then discs just add weight and cost more.
If you have a hill so steep that you had to get off and walk, odds are if you get the same gearing you still will have to get off. Check to see if you have a cassette on your 7100 with a 34 tooth cog. I believe the 7100 is a 7 speed, but Shimano makes 7 speed cassettes with a 34 tooth cog, combined with your 28 tooth small chainring, you shouldn't ever have to get out of the saddle unless you spin out.Being a student you probably are on a low budget so that is something you could look into before buying a new bike. That 28 X 34 gear is easier than walking.
As far as fork goes, Most on these boards will tell you suspension forks will slow you down. I'm presently riding a rigid hybrid after 8 years of putting lots of miles on my 7300 with suspension fork and seatpost. I can't tell any differince in speed and find times when I miss the suspension fork. With all the weight your carrying, the differince in weight between suspension fork and rigid fork is insignificant. If you stay with the 7100, to help with speed, try a set of 700 X 32 tires, as I said above, they'll feel squirrly at first, but you get used to it.