You will be surprised to know that this is more common than you may think so don't take it personally.
I have been on the giving and receiving ends.

--- GIVING END ---

Armed with research "how to kick out a co-founder" you approach this person and tell them that you are letting them go. The first time I did this, I never gave them notice and blocked access to the work. They never mentioned this to me, and they have never talked to me ever again and have therefore effectively burnt a bridge - it was so bad, I did a presentation at an event once and the guy walked out to "buy his meds".

The second time I've had to do this, I am nicer now and gave this person written notice in advanced as well as an opportunity to draft an agreement as well as an actual discussion of said agreement.

--- RECEIVING END ---

Now, I was on the receiving end although the mental dissonance was not so great as it was a partnership. I knew that it was not going well BUT being on the receiving end is complete rubbish. Even after nearly 3 years, I wouldn't event want to have coffee with these guys.

--- BACK TO YOU ---

You mentioned that you played a central role in the product concept, strategy, legal approach AND coding which means that these two 'non-devs' were not that essential. Which begs me the question as to why you were not the one to kick them out in the first place. The only excuse would be if the original concepts have changed over time it would also require you to change your mind in regards to the development of it. It's like being in a rock and a hard place for the 'non-devs' if they need to get permission or approval from the coders (ie you) regarding the product. It's a power thing. The non-devs don't want permission from you. And you know that you don't have to code their suggestions. You are the product because y'know, you're the dev! Maybe that's another reason why they wanted to kick you out - they simply just don't want you in their group (starting to sound a bit like high school...). I had a discussion with an entrepreneur friend of mine (business guy) and his answer was "the technical guys will always think that they can do it all themselves".

Keeping in mind the unpleasantness of this situation there are some things that you did good. For example, not signing the IP transfer agreement (and keeping it) which indicates that they recognise your IP in the first place. Asking for equity share to be written down. Reacting in a mature way by requesting to be paid for your consultancy fee - although keep me updated if you go through with this. It has happened to another friend of mine - he was with their company for several months, the business guys had senior positions in big companies like BSkyB, used his savings to move to another city. When things didn't turn out, he tried to claim a consultancy fee but was laughed off! I swear anyone who has managed to work within the upper rings of big corporations is a sign of psycopathy!

Now what are your options? Open up a start-up featuring your product. It is still your IP. You may need to get 'non-devs' on board so this time around try to have some sort of written agreement in place. The thing with this current group is that if the non-devs play their cards well, they'll hold up the front well enough to get some investment, and through that be able to purchase coding talent to fill in the gaps. Eventually, down the track, the product that was previously 'yours' will turn into 'theirs'. Welcome to the circle of life!!

You can also nurse yourself with the fact that most start-ups will fail including this one. So if you think that the product is good enough, then yes, go ahead and start-up. Don't focus too much on your new competition and just add this in your things to learn pile.

Another thing to keep in mind is that if you startup with this product it will only provide a bit of extra validation and will probably push the other start-up to do better. So think about doing this in stealth mode and go public when ready. I know because this move has been done ;)