Lee von Kraus answered:
Option 1:
Generally when you're first testing out an idea, you want to build a first functional prototype cheaply and quickly. The easiest way to do this would be to use existing tools that facilitate what you want to do. For instance, you could make a web-based version (which you could embed in an app too if you want) using Marketify, as described here: http://goo.gl/2kSkUm.
----------------------------------------------------------------------
Option 2:
If you want to skip straight to investing a lot of time and energy into testing the idea, then you'd want to find, or be, a developer for the platform of choice. Either iOS, Android, or React Native (both iOS and Android). Find someone that has experience in databases (would be needed for saving profiles, products, etc.), or, if possible, in marketplace type apps.
Whenever you assign them a task, break down the task into small chunks. Make the chunks as small as you can (within reason, and to the extent that your knowledge allows), and tell your devs that if any chunks seem large, that they should further break those chunks down into bite size pieces.
For instance, for the overall task of making a new webpage, _you_ might break it down as follows:
1) Set up a database
2) Make a form that takes user email, name, and phone number and adds them to database
3) Have our site send an email to everyone above the age of 50 each week
When your devs take a look at it, _they_ might further break down the third step into:
A) Set up an email service
B) Connect it to the client database
C) Figure out how to query the database for certain users
D) Have it send emails to users over 50
You can use something like Trello to assign tasks and keep track of progress. In Trello you'd set up 4 columns titled, "To Do", "Doing", "Ready for Review", "Approved" (or combine the last two into "Done"). Then pay them and track their progress.