To keep the project organized I use a program/website called ClickUp to write out every task I need to do to finish the game and give each task a time estimate. I tally it up and base the release date guess on that.
Long story short, I made some spreadsheets to chart out exactly how much money I'd need to be able to pay bills and work full-time on BGP for 18 months and based the Funding Goal on that. No such thing as too much money (as far as I'm concerned) and any extended budget beyond what was planned would go towards marketing efforts and hiring professionals to help make the original vision without extending the promised scope. Not getting enough money means I have 2 more months to try again, otherwise surrender the dream for a bit, work a paying job and try again in 5 years once I stabilize money-wise.
At the end of that timeline I ran out of the money, got better at organizing and predicting how long things take with experience and found out I needed another 18 months to actually finish the game. So now I'm getting by using a scary amount of debt with the new DEADline of March 2024 being where I either start to make all the money back or ruin my life financially (great motivation to do the work required).
So it all comes down to experience (from making 7 mobile games), good tools (Unity, Clickup, Discord, Google Docs, etc.), and ALWAYS assuming things will take 3 times longer than you'd originally think.
Something ALWAYS goes wrong and you need to be prepared to roll with the punches. Always have a plan B, C, D, E, & F (heck, even G)