No, no and NO. A giant breed isn't a good first dog, period. Just looking at the possible money you need to have to take care of a giant breed, is prohibitive. I couldn't have covered even the maintenance of my EM at your age, and the training required is also something you need to take into account. It isn't just about walking the pup twice a day, it is about having some training experience and a strong set of boundaries.
I hate to sound so negative, but the CC needs a very strong, experienced owner. You aren't there right now, and in the end, the dog will probably suffer. It isn't about getting the best, or toughest looking dog, it's about getting one you can train, and take care of adequately. There are too many mastiffs in rescue situations, because people got them as a status symbol.
I am not trying to insult you, just trying to let you know that this breed needs an experienced owner.