What factors to take into account when choosing a hybrid bike?
A couple of things I would advice on. 

Firstly, from my understanding hybrid bikes tend to be very upright and commonly with front suspension. Have you looked at any touring bikes? 

Hydrauclic brakes: Yes, they are usually better than mechanical ones. Although there are some very good mechanical ones too, look at TRP's Spyre or Hy-Rd for example. Hyraulic brakes come with their own problems too, which you should also consider. They are usually more expensive to maintain (liquid and tools cost more than cables). They are also not great with sub-zero climates. 

Carbon forks usually have better shock absorb than aluminium, but steel forks are cheaper, have arguably the same shock absorb and can easily load them with pannier if needed.

You should be able to get a good entry ridgid steel bike for that price, if I were you, I'd buy the cheapest second hand steel rigid bike and use it for a while. You should then learn enough to be able to buy a suitable bike for yourself in the future, using your experience with the cheap bike as a guide. 

You should read this article Best commuting bikes as it gives a detailed description of the different choices for commuting bikes. By looking at the bikes they recommend, you should look at what you might like from them, flat bars vs drop etc.