Here’s a link to a spreadsheet with two tabs. One that helps you calculate flour quantities and hydration percentages and the other with a simple baking schedule (assuming you store your starter in the fridge and are only baking once every week or so).
There are more complicated dough calculation sheets but many are way over the top. The instructions are on each tab.
Please make a copy of the spreadsheet before changing any values!
By the way, you can also alter flour and other ingredient percentages but the flour percentages should always add up to 100% (that’s how baker percentages work). For example, say you wanted to bake a loaf only with white and rye flours, just change the white percentage to (say) 85, the wholemeal to 0 and then the rye to 15. Or if you wanted to slow down the fermentation process you could use a lower percentage levain seed or inoculation by reducing the levain percentage to 10 or even 6%.
Let me know if you have any questions.