I don't think it being a lab mix will lessen the amount of energy the dog will have. Labs are pretty active dogs as well. Vizsla's are extremely energetic, but like any dog, as long as they are properly exercised they lounge around the majority of the day. We give Coya an hour long play session at the park each night and a walk or 2 during the day. The rest of the time she is usually on the couch or in the bed (under the covers of course!)
With that being said, IF Coya isn't exercised properly she can be a real handful. When we had her spayed and had to keep her activity to a minimum it was the hardest 2 weeks since we had gotten her at 8 weeks old. If you have ANY doubts whatsoever that you won't be able to give the dog what it will need, do yourself and the dog a favor and wait.
I am in my early 20's as well and I have an extremely busy schedule working and going to school. Luckily I live with my boyfriend and we both share responsibilities for Sequoia. I feel if I were to have her on my own it would make things A LOT more difficult and A LOT more stressful. You need to take into consideration the time you are going to have to give (and give up) for the dog. Since having Coya she has become our first priority and we have had to work around her and her schedule. Another thing you need to think about are finances. I noticed you have listed the big expenses such as vet visits but you also need to think of the seemingly not so big ones that add up quickly: crate, food, bed, leashes and collars, flea and tick meds, heartworm preventative, chew sticks (especially for the teething months), etc.
As far as crate training it really depends on the dog. We lucked out, but I have heard some horror stories. My best advice is to start right away! The crate is Coya's comfy spot. She is in it at all times when we are at work/school/or out and about (no longer than 4-5 hours). Sometimes she will even go in for naps when we're hanging around the house and the door is open. I feel as long as you do it right you should be successful.
The last topic I will touch on is the space. I know you have a concern about having a dog in an apartment. I won't lie, a house with a yard is the ideal home for any dog, but as long as you are able to take the dog out to use the bathroom, for walks, and heavy play, I don't think apartment living would pose as a problem. One thing that I have read about here on the forum is separation anxiety in V's. Sometimes it can become extreme and can lead to excessive barking when their person isn't home...definitely not something your neighbors would want to hear when you're out.
I know that was a lot of information to take in, but I wanted to answer all of your questions and share some things that may make or break your decision. Do your research: look online, ask other dog owners, and read books! Good luck to you!