Fill in what you have — each widget activates on its own as you connect it. Nothing is sent to any server except the services you point it at.
1 · Trello (works immediately)
Get a key + token at trello.com/power-ups/admin → create a Power-Up → API Key tab. Copy the key, then click the Token link → Allow → copy the token.
2 · Estimator & Scheduler links
Paste the URLs your dashboard should link out to.
3 · Live business data (QuickBooks + Gmail)
These need one small backend. Paste your Google Apps Script web-app URL once it's deployed — it should return JSON like {invoices:[...], gmail:{...}}. Leave blank for now; I'll hand you the script.