Great questions folks. I believe I have lost to most of you at least once before. I greatly enjoy our game, but am not a particularly competitive game player. Unlike my gf Eryanne who likes to crush it.
I'll try to answer all of these questions here:
1.) One question that I have is how do you keep all the art to match the same C&C style? How could I learn to do a similar cartoony-style art that looks like it fits the game?
This has been a challenge for us from day one. The original art team, all quality artists whom we wouldn't be here without, had all their own very differing art styles. Another challenge we faced was that while the original style that worked for our units did not work well for our cards. Eventually we sat down and wrote a design document with specific rules from head and hand size to stroke style and color, and did our best to apply the guide to both units and cards. Most of our content since Tournament of Champions adheres to the guide which is great, but as most of you can very obviously realize, the older content, both units and card will look out of place. (More on that later.)
I'm an art school teacher, so I will always push education if you're considering this field as professional artist. Art is just one of those things that you need to study and practice, and really absorb the history. There has never been a great artist who didn't improve by going to art school, even if many great artists left art school. It's all about understanding what's happened before and going on now, as well as exploring technique and physical skillsets. I have two degrees, one in Game Art and Design and another in Digital Design and Production, and I consider myself a designer more than an artist. I really attribute a lot of my success to mastering graphic design before anything else.
That being said, I'm a big believer in the idea that quantity eventually leads to quality. Draw, draw, draw, all day and all night. It's not the most helpful answer, to that question, but it's really the only answer. Draw until you hate it, and then keep drawing because that's the point in which you learn to love it. If you don't love it, it will always show.
One last note on that, if you are considering an art career, just know that it is by far the most abused craft in entertainment. The hours are unforgiving, the pay is not comparable to programming or production, and it's easy to single out art as the problem with a game (either not good enough or too bad for the audience). You do it because you love it. You do it because you have to do it.
2.) Do you use a drawing tablet? What kind and what software do you use to draw in?
I use a Surface Pro 3. I adopted the Surface Pro after using just about everything out there and I haven't looked back. Microsoft is making the best hardware out there for artists right now. Skip the 4 and go get a cheap 3 on eBay. It will last you at least 2 years. Skip the Surface Pro 1 or 2, because the technology is outdated (wacom vs ntrig) and unsupported, and there isn't enough of a big change between the 3 and the 4 to pay the premium right now.
3.) What do you think of some of the older style art that doesn't fully match the newer art? (Cards such as Burn, Darkfire, Blade of Light, and Brewery) Do you plan do redo or update any of those to fit the new style?
Any plans on updating the old arts to match new art style?
Would love to see more updates for old cards to get them in line with everything else. Loving the sprite revisions for Archer, Barbarian, etc.
This is a general theme that is near and dear to me, but it's a complex situation. Production art is a very different beast. When so much of your life is invested in the success of a product, and the stakes are so high, you really have to spend time on things that make the most sense, and unfortunately the older art doesn't break anything and doesn't need fixing. The pure artist in me hates that response, so the simple answer to this question is, whenever there is unused time on my hands, I would be working on these things. Just to give you some insight here are some of the things that come up when we talk about this internally.
Updating units would be more important than updating cards. Cards are on the screen for a shorter amount of time and they are inanimate.
That being said, units in our game have a visual lifespan of 1-3 rounds, so they aren't on the screen for very long either. 
Cards are easier to make, however, due to the nature of game design and balance, both need to be perfect in order to make the best card. Color, style, story, character relationships, etc. All of these things can easily feel out of place if the card is cut and held for another expansion, redesigned or rebalanced, moved to another faction, or anything else that come about. It's just not realistic for all of these things to be designed perfectly AND never change. This is why Maddy looks different than his mechanics would suggest. This is also why some cards like the Stalker, which was originally designed as a Warlock, looks out of place as a Neutral unit.
People can deal with balance changes. It's the nature of the beast. But when you change someone's art, the response is unpredictable. People attach to content because it is the source of emotional and imaginative investment. In my personal experience, changing art out from under players has been a very tough sell. When someone loves something, it looks perfect to them, and so my idea of improvements may never meet their expectations.
The most important idea we hold here, is that it doesn't matter if your art is good or bad, if it's inconsistent, then it will always be bad. So yes, this is something we think about and plan to do, but it's just a matter of time and resources that determines when and how it gets done. I would love it to be perfect.
What's more important then the little details (or lack there of) is the overall feel of the style. If the art emits the right emotions, then it's going to fit in the world, even if it doesn't look perfect.
Thanks for the questions guys keep em coming!
How important is the character (unit or card) art to you when you play this game?
Have an art question? Ask away! 
