Your biggest expense is obviously gonna be your boat.
If you just bought a fresh rig, insured it to the hilt, and are stressing over shelling out 300.00 every 4 months for fresh batterys, or replacing a 700.00 trolling motor once or twice a year is gonna worry you..... just forget it.
The expenses even if you get lucky and don't blow a powerhead in your first couple of years are outlandish.
You are going to wear out lots of equipment WAY SOONER than you can even imagine, and there will be no sponsors to help with any of that for quite some time. Having your boat/motor covered under warranty just means that your down time will be longer when a component fails.
In this day and age you are gonna need good credit, a new boat, a fresh truck, a rich daddy, and friends in all the right places. Otherwise you'll be worrying too much and won't be able to concentrate on your fishing like you need to.