Ideally, you have LOTS of condensation, it literally could be gallons per day. On some days, with my mod-con, if I'm in the basement, you can literally hear the water flowing through the pvc outlet pipe from the thing and the condensate pump's float switch is tripping regularly.
That vertical leg would only be acceptable (and maybe not, depending on the specs of the device you choose) if the device had its own condensate pump and collection system. You want to avoid 90-degree bends (excess ones, anyway). Each manufacturer will list the maximum 'functional' length of the air inlet and outlet - elbows equate to a pretty big length.
Bottom line, select your equipment, then follow the installation manual as to how to run and terminate the connections or you may just be doing it over again. Personally, I'd prefer to have the condensate collection in the unit. Depending on where you can drain it to, you may need to buy the optional neutralization kit for the burner you choose. This is normally only an issue if you have cast iron or copper drain lines (well, if you have galvanized, you've got other problems).