.) yes, htc lighthouses will work with the headset. Version 1.0 and 2.0. but if you use 2.0 lighthouses you have to use same version handcontrollers (in case you later on want to play some more than only seated)
.) yes, i can confirm tracking works with only one lighthouse flawlessly. I didn’t test with handcontrollers and one lighthouse, only with the headset on a simrig.
.) depends on the speed of manfacturing and quality control of pimax. I would guess around end Q1/beginning Q2/2019
.) almost same for the lighthouses, maybe even little later. I assume valve right now is holding the v2 lighthouses back to bundle it with their headset which they probably announce soon (CES?)
.) very likely because headset is ready but Pimax version (housing) of lighthouse v2.0 not. If pimax decides to ship htc branded lighthouses they could come together. Depends on htc and Pimax.
.) eye tracking was a promised feature of 5k+ and 8k. It should be released as soon as the hard- and software (foveated rendering support) is ready. I do not expect it to arrive in H1/2019. likely later.