eLearning development professional and Lead Architect of LearningCart (www.LearningCart.com). 10+ years experience developing courseware and SCORM compliant LMS systems.
I think what you face is the proverbial challenge startups run into of how do you demonstrate value without users and how do you get users until you have value.
Online training is a great niche market with the opportunity for huge profits. At the same time its an increasingly crowded market place so you need to really focus on what is going to differentiate your business (see: http://sellyourcourses.com/is-selling-your-courses-a-good-idea/).
If I were you I would focus on content first. If you are willing to invest in taking the trainers material and building an online course out of it and sell it on you platform there isn't a huge down side for the trainers. That process can take a while and be pretty involved so you are offering to do a good amount of work at no cost. In that instance 50/50 seems fair.
Udemy's model works better if the trainer is on the hook for developing all the content since they are doing the leg work - but honestly if the trainer can do all of that there are a lot of different platforms they have at their disposal to sell their content.
In any case I would start with a few key courses and get a minimum viable product online. Don't start by trying to build a huge library. Get a few courses online and see what happens. This will allow you to validate your idea and you will learn a lot based on the feedback you get.
There are number of different platforms that are designed to help you with what you are after that provide a varying degree of functionality. Some focus just on the LMS side of things, some focus more on marketing, some like our platform LearningCart (www.LearningCart.com) try to provide everything you need (website, LMS, ecommerce, reporting, etc).
One thing many people don't know when they get started with elearning is there is actually a standard for developing web based training (SCORM). Although it sounds great to use a tool like teachable, those sorts of tools are using a proprietary format that locks you into their service - If you ever want to use another system you must rebuild ALL your content.
If you develop your training using SCORM you can take your content and easily load it into the 1000's of LMSs that are SCORM compliant. Long term it gives you options and it also lets you much more easily license your content because most large corporations (and schools) are already running a SCORM compliant LMS internally. Some of the popular SCORM compliant course authoring tools right now are captivate (by Adobe), articulate, and ispring. These are desktop applications that are way more powerful than the web based authoring tools and have a long track record of support and feature expansion. Again if you develop your content using one of those authoring tools in the long run you have will a lot more control and options.
Hope this information helps, happy to answer any follow up questions you might have or setup a call to honestly assess your needs and recommend what platforms might be a good fit.
As everyone else mentioned its a challenge to find an experienced developer willing to work for equity alone. The longer you have worked in technology, the less likely you are going to be interested in an equity only deal.
That being said, if you idea is patentable and you are able to secure a patent on it, that would make an equity deal (if it included partial patent rights) much more enticing. If your idea isn't patentable your best chance of getting someone interested in an equity deal is to go after entry level developers. They maybe more willing to take a risk as they build their portfolio and get good real world experience. Craigslist is definitely an option for reaching those sorts of developers, as are developer focused meetup events, and of course college message boards.
Hope this helps!