Consider not only freelance developers but a freelance "scrum" type team with a PM or PO. Vet these carefully as a bad PO will sink the project. A good PO will gather requirements, keep the team on track, report back progress etc. Since this is an outsourced solution you must be "waterfall" as in be crystal clear on how the app will work, what is the business logic (the devil in the details) etc. Freelancers will not stop to ask questions or clarifications. They will do exactly as asked no more or no less. While I do agree if software is not your core competency you should not bring it in house it is worth mentioning most software starts as an in house solution that is then upgraded to a commercial offering in the B2B space you operate in. Its a long shot but if you stop thinking of your software as a cost center but as your actual core competency its possible to turn it into a revenue stream that is some cases outstrips the original company. I would say at least 95% of the attempts to do this fail though so don't take it as granted.