Make.com expert for creating custom Slack App with Oauth2 & Modules

I need someone proficient enough in creating custom apps within make.com/apps

First, I'm testing this with Slack, so I already have a Slack app for testing,

App ID
Client ID
Client Secret

Part 1: Ouath2
Edit the jsonc variables so the Bearer connection works

Part 2: Create modules within the app with the slack API endpoints
One for getting all the channel IDs: https://slack.com/api/conversations.list
Another to get the conversations: https://slack.com/api/conversations.history

(A plus if you know how to implement timestamp for this last endpoint: Current timestamp latest_timestamp = time.mktime(now.timetuple())`)

In short, at the end, the custom app should be able to allow non-make.com users to allow access their slack data via Oauth2, so the token is used to authorize the modules within the app to get the (1) channel ids and then (2) channel conversations.

Then I need to figure out how to implement the token refresh, so the user doesn't need to allow the app every time.

Please give me an estimate for a fixed price or a realistic total estimated number of hours.