If I purchase the model that I can afford right now, will it be up-gradable to the model I really want, ie: more range, more solar etc...

I am highly confident that upgrades will be possible, but you might not like the price. I am saving my worries for things like 1. Will the models actually launch. 2. Will Aptera remain a going concern.

I read in recent answers to hundreds of questions,,, To be determined on things like batteries and AWD etc