A note about buying and selling technology:
In most strategy games (not only including Paradox games) I've seen this feature implemented in, technology has been a cause of severe unbalancing without severe restrictions on its use. This is mostly due to the coordinated research we see in these games; players who are able to exchange technologies can quickly outtech the opposition by coordinating their research efforts so that they gain a multiple of the technologies they would otherwise get. While there might this feature may become a part of HoI2, I advice you to not become too excited about it before you know what necessary restrictions will handicap the trade. In Victoria for example trading techs cost research points (which can accumulate due to a minimum research time for each tech). Perhaps there will be something similar for HoI2.
In most strategy games (not only including Paradox games) I've seen this feature implemented in, technology has been a cause of severe unbalancing without severe restrictions on its use. This is mostly due to the coordinated research we see in these games; players who are able to exchange technologies can quickly outtech the opposition by coordinating their research efforts so that they gain a multiple of the technologies they would otherwise get. While there might this feature may become a part of HoI2, I advice you to not become too excited about it before you know what necessary restrictions will handicap the trade. In Victoria for example trading techs cost research points (which can accumulate due to a minimum research time for each tech). Perhaps there will be something similar for HoI2.