I’ll have to flesh it out and see where it goes.

I clarified above. If you have 2 remaining HD and they are d12s. Then you could roll 1/2 of you remaining HD (1d12). This would not spend HD. It only affects 1 creature. So the Jedi would have to choose himself or another creature for the healing during the short rest. And it’s once per day.
A Monk already has self healing of 3xLevel once per day, so I would think that this is usually used on others…maybe.

Okay, doubling attacks is not the best term to use and Action economy should not exclude other actions. So basically the Jedi Haste doubles speed, and adds an Action (Attack, Dash, Use Object, or Hide). Costs 3 Ki though and only lasts one turn, but at 17th level seems to not be overpowered. Unless I missed something else. My vision for this feature was mainly for quick Jedi movement.
So if you have 2 attacks for an Attack Action, then you could use it to make another Attack action for a total of 4 attacks, and then as an option 1 unarmed attacks (2 unarmed attacks as a bonus action by spending an additional 1 Ki point with Flurry of Blows)

Force Healing:
Let’s say my Hit Dice value is 12, and I have two remaining Hit Dice…
can I heal myself up to 12 points of damage? Are any Hit Dice spent in
this process? How many times can this be performed in a single short rest?

Jedi Haste:
Does doubling the attacks do literally just that? If my attack action allows two attacks, do I now take four? or is something else implied by this?

P.S. Awesome stuff you’re doing here with this site.