Ongoing File Transfer App Development

We're looking for a team to quality check all the features in the app, ensure all features are working well and efficiently and be able to test and release patches and new versions. Some features we are looking on improving what is already there for example a more in depth share folder system. Some new features we had in mind are a better contact management system. Potentially a form of cloud-storage intergration with a user's own AWS.

This is currently what our last dev said is in use in the app:
SnapBit Client/App :

Electron - v4.x - https://www.electronjs.org/
NodeJS - v10.16.0 - https://nodejs.org/
Socket.io client - v2.3.0
Less - v3.x - http://lesscss.org/
Electron-builder - v22.3.2
Electron-updater - v4.3.1
C++ - std-c11 - https://en.wikipedia.org/wiki/C%2B%2B11
UDT - v4 - https://sourceforge.net/p/udt/git/ci/master/tree/
Crypto++ - v8.20 - https://cryptopp.com/release820.html


SnapBit App-Server :

NodeJS - v8.8.1, using Express 4.16.x as the web-server.
PostgreSQL - v9.6.x, connecting to AWS RDS, using KnexJS 0.12.x as the SQL driver. - https://aws.amazon.com/rds/ - http://knexjs.org/
Socket.io server - v2.2.x
SendGrid - v4.7.x - https://sendgrid.com/
Stripe - v7.8.x - https://stripe.com/
SSL is provided for free, by https://letsencrypt.org/

If you decide to take this project on how do you keep track of the work you do and the time you spend for invoicing us?