My solution for this is rather simple. You simply focus and categorize melee into sub branches and apply those "Elemental" or "Different rules" to each kind of physical weapon and put it on par with a magic counterpart. Allow me to give you an example.
Say you have a shield. Well that could be pretty much it. My kind of focus would be to ask, what kind of shield? is it a wooden shield?
A wooden shield would be very poor when defending against melee... but perhaps it can be useful when dealing with Energy/Electricity-based magic users.
Then it comes the problem of fire magic! a whole world opens when you "Corner" your player in the non-magical role.
Sounds pretty good, I think in combination with the different abilities you mentioned that this is a pretty solid concept. Whether or not it's actually fun will depend on the specifics of your actual implementation, but it's certainly a foundation with the potential to be very fun.
As for your difficulties with making a prototype, if you have trouble with coding I normally recommend looking at tools such as Construct 2 or Game Maker which can allow you to do some or all of the work of putting together a simple game without coding or with only minimal scripting in a highly simplified language. In the case of this particular idea you might even be able to create the final game with such a package, but even for more complex games or those with more difficult performance requirements it can still be good to put together a small prototype to play with your mechanics. As an added bonus it can also help with explaining and marketing the idea later on.
You're right about "the idea guy" though, and I think what you're doing by working to fully detail and document the idea and begin creating content is an excellent step in the right direction.
Can you elaborate on the non-combat quests a bit more? They sounded like a reasonably important part of the concept, but aren't really detailed at all -- will they be mini-games, simple "reach the place and pick the dialogue options" mechanics, or something else entirely?