while there may be other good reasons for doing Mars first expeerience in colonization is probably not one of them. if our telescope spying and or probes detect a breathable atmosphere coupled with a magnetic field/ionosphere then the difference between the two are so great that Mars is like colonising hard vacuum and the other is like colonizing australia.
Mars should be done. not least of reasons is that it is much closer. but it is likely that the only knowledge Mars would impart appliocable to colonizing a more earth like planet would be getting there and psychology and logistics.
Actually that is exactly the reason why i would propose to a conlonization effort of mars first. It is inhospitable to say the least, and exactly what we need to prepare. I was always raised to prepare of the worst even if you knew it wouldn't happen. A colony ship going that far away (a short distance on the galatic scale) has no recourse if an emergency were to befall its mission or forbid its final destination, whether it be some kind of ecological disastor on said planet that causes it to be in hospitable, or as nem put something as simple as allergies that would prevent us from even breathing unfilitered air or going outside without protective sealed garments. Such are the lessons we shall take from mars, a possible worst case scenario so to speak, preparation so that our colonists will have some expiernce to allow to them act in a manner in which to perserve the mission and ultimately their lives. Mars also lets us learn how to set up a colony with minimum logistics and minimum supplies for the mission at hand. It also give us the knowledge we need before even thinking about colonizing a world far enough away that it would be impossible for us to peform any kind of rescue mission. Further we must have trained people who know what to do, and that training simply put can only come from expiernce, as no simulation is going to give them the breathe of knowledge neccesary to handle the variety of situations that will most likely befall them.
So i would counter that all the lessons we would learn from mars perfectly applicable for any other colonization effort, and not just for the few reasons you listed.