What you need - and pretty desperately - is a partner or technology advisor that is dedicated to your company and at least has review oversight of the work being done by the contract house.
Your question to some extent belies your lack of understanding of the technology process. A CTO or a Chief Architect or a Technical Advisor - is someone who's job it is to
a) understand and embrace your BUSINESS goals - both short term and long term
b) properly balance - or help you at least understand the tradeoffs for you to make the call - on short term implementation tradeoffs vs. long term roadmaps. For example I suspect that your evaluation of "cloud platforms" was done largely on price and ignored the costs of scaling to what your mid-term operational architecture will need to look like
c) give you insights into technology trends and competitive offerings in the marketplace
d) help you understand and develop your Intellectual Property
No contract dev house will give you this. and without this you are at great risk. OTOH.. once you have this advisor - you really do not need inhouse development.
how to find such a technological co-founder? Incubators, entrepreneurial workshops and also just plain hiring. No it won't be cheap. Particularly if you are going to only pay with equity.