have in retirement? 100k/year? 80k? 120k? Or if picking a certain number per month helps, go with that.

How much money will you need saved up in order to withdraw that amount each year in perpetuity? 2 million? 4 million?

How much will you need to save to get to that amount by the time you plan to retire? If you can't feasibly save that much, you'll need to compromise on either a) when you retire or b) how much you hope to have saved up (and, by extension, how much you'll have available to withdraw) by retirement.

There are online calculators that can help give rough estimates. Probably better to overestimate how much you'll need saved up, and for good measure don't rely on SS income; treat it as icing on the cake.