Hard to Start 2007 Altima

P0300 is the code for a random misfire, with this in mind, i would first check that the coolant temp sensor is ok, as it starts ok hot this could be the issue, i would start here and let me know who it responds.

Should I just ohm test the senor or try to pull live data from the ECM with my OBDII reader?

You can do this, but you will have to get the temp scale for correct Ohm readings, i have had a look and it is not on Mitchel 1, if you can get live data this will give you a better idea as to what is happening with the entire system.

Of course tonight when I got home tonight and hooked up my scanner it started right up with no problem. The temperature went from 82F before starting it all the way up to 265F after running it for awhile. Only differnce between today and yesterday is it was in the shaded garage all day. Not sure what to try next, espically if I can't recreated the symtoms. I'll let it sit in the sun tomorrow and see how it reacts. Weird. Any other parameters I should watch on the scanner if I can get it to misfire again at startup?

265 degrees is pretty hot for an engine. If you have a cooling system thermometer, check the temp of the coolant in the radiator.

Check the cold start injector to make sure it's being actuated.