The boards that we received are running quite hot, and I decided that we cannot sell them without heatsinks.
Q1: Can they be undervolted to prevent overheating and add the heatsink later ?
Do you think it's a good idea to do preorders on this new hardware or should I list it on the site when they're ready to ship?
Pre-order is fine, you have earned my(and probably a lot of others) trust.
If you add them to the shop, and if the answer to Q1 is yes, can you please also add them without heatsink for a slightly lower price. [ I would add a clear warning that they come as is (no guarantee) and require undervolting or forced cooling and a heatsink ].