My brewsmith setup says I'll lose .5 gal per hour in boil. I am assuming that's super low based on what I have read, maybe closer to 1 gal
Best thing to do is a test run and measure your boil off, .5gal per hour is low for a kettle appropriate for a 5gal batch(10gal) if uncovered, 1gal per hour is reasonable if you are not creating a volcano type boil. The diameter/surface area of your kettle pretty much determines the boil off if you are uncovered.
What were your kettle and fermentor loss set to in beersmith? If you plan to dump everything set kettle loss and mashtun dead space to zero and maybe .25 to .5gal for fermentor. If you had a lot of hops it will not compact as much.