A few thoughts here...
First, NO ONE is perfect and the grass always seems greener on the other side. IMO, when choosing a partner it's important to keep a reasonable perspective. I'm not suggesting that anyone should gloss over or ignore the "deal breaker" traits, but certainly keep in mind that if you were to move on to the next guy, he could be a great go-getter, but void of other admirable traits. He could be stubborn...or controlling, and you could be constantly butting heads. A laidback, easygoing, over-achieving multi-tasking go-getter is kind of a tall order. You don't typically find those traits all in one package. Read this forum, talk to the women in your life and you'll find out pretty quickly how unfulfilled and unhappy so many of them are because of serious problems with uncaring, emotionally stunted, stubborn men. A man who treats you well, engages in discussions about the relationship, admits his faults and works to be a better human being is a GEM of a man, truly.
And as women maybe we need to be honest with ourselves. Again, take a look around and pay attention to how mothers raise their sons vs. how they raise their daughters (especially our parents' generation). Boys are babied and frankly mothers are guilty of failing to teach male children basic tasks of self-sufficience. Yet we've moved away from the stay-at-home mom culture, so women now more than ever are taking on ridiculous stress and responsibility as they work, take care of the house, keep the bills in order and raise the children.
In your case, it sounds like your fiancé was never really forced to take care of himself fully on his own, and his parents didn't give him the tools/education to handle his finances and household tasks appropriately.
All that said, I'm not suggesting it's our responsibility to just put up with it or to teach immature men how to be self sufficient adults. I'm just trying to throw some perspective out there for anyone who is quick to throw the guy under the bus.
anssett, it sounds like your fiance and the relationship you have with him has redeeming, wonderful qualities. You have a lot of questions to ask yourself before you marry him. Totally recommend continuing the relationship with him and learning more. It is awesome that you both are so self aware and able to have conversations with each other to assess the relationship and how you both are feeling. IMO that is a hugely positive dynamic to have. Let's just call it what it is - you're Type A. :) Have you ever dated a Type A guy and experienced what it might be like to be in a relationship with someone who is similar to you in that aspect? Are you able to relinquish control? Are you comfortable letting go of certain responsibilities to be handled by your partner?
Echoing what others have said, there is potential (with time and marriage) your fiance will eventually come to resent you if he feels 'beneath' you. And you are likely to become resentful of him if he doesn't meet your standards. Resentment is toxic, so be conscious of the potential for it.
People do grow, but your core personality doesn't. You have to decide whether his personality is one you can live with, while being realistic that whomever you end up marrying is going to have faults. It's just a matter of finding the one whose faults are the most tolerable.