Yeah, I already use Github and Trello for Project management and I am also available during PST/EST/GMT/MST timezone, So you can expect daily updates and weekly meetings from my end.
As fro the tech stack, I can use WP as well as can you open-source framework to design and develop a portal for invoicing and contracts and connect it Docusign, So it's all up to your personal preference.
Let me know when you are available, so that we can have further discussion.
Regards,
IR.