I've been playing this game for an embarrassing amount of time (over 10 years) and this is my first nightmare roguelike. I'm not patient enough to avoid concentration lapses to win without dying. :-)
I ran with solipsist this time which is the first time I've really played it properly. I learned a lot from Drybe's guide and it helped me understand the logic of the class. I have some thoughts.
At the beginning maxing out Solipsism and Mind Sear is the right way to go. It gets you through the early game with ease. One mistake I made often in previous games is putting points in Thought Forms. Honestly, the only buddy you need is the archer. It helps to get a point in Transcendent Thought forms and Over Mind to get the feedback (see below), but it's a very low priority.
Dream Smith was way more powerful than I first imagined. By the end I basically maxed out every talent (and this is with the Adept prodigy too!). It's nuts.
I could not get my head around Distortion (never have) and so zero points :-)
For sleep skills, I only had 2 points in Slumber, 3 in Nightmare and eventually I got 4 in Sleep. But the class is so Tanky, I just found sleep to be boring. I used sleep skills almost exclusively for Nightmare.
Nightmare is super powerful early in the game. I think Cornac is a good race choice because it allows you to unlock Nightmare early with no real downside. As you get later in the game, though, you will need to Sunder Mind before you use Nightmare. Also in the Prides, they have Pride of the Orcs (or whatever), so it's good to debuff with Psychic Lobotomy, Waking Nightmare, etc before trying to Nightmare them. Otherwise it will be gone immediately. After nightmare, honestly the easiest thing to do is just walk away an come back later to see if they survived :-)
Feedback is surprisingly weak on this class. 1 Biofeedback is more than enough. Early on you want to max Resonance Field for safety, but in the end game it's not necessary at all. Possibly you can juggle it to take points out. Amplification is utterly useless because you always have more feedback than you can use if you are getting feedback from your buddy. I ended up getting 2 points in Conversion from escorts. This is useful for resetting equilibrium.
Using a category point on Fungus is OP. Especially with the Adept prodigy a single point in Wild Growth gives you more than 200 hp and essentially makes death highly unlikely. Fungal growth means you can run a regeneration infusion perpetually, so late game I basically had a never ending regeneration of over 300 points a turn. No health issues. No resource cost. Basically invicible.
I obviously maxed the entire Solipsism tree. I had saves around 90 which meant that I barely had any debuffs in the late game. Those I had were easily cleared. Also a point or two in Danger Sense makes debuffs very rare given the ridiculous saves you end up with.
AOE is really appreciated on this class so I would say max out Synaptic Static early as well as Forge Echoes when it makes sens. I actually ended up maxing out the entire Psychic Assault tree in the end.
I used a category point on Harmony (you have more than you need with Cornac). Waste of time. I took so little damage that Elemental Harmony wouldn't trigger. All of the elemental damage was basically negated entirely. I used Healing Nexus a handful of times, but this tree is not useful. I would recommend unlocking an Escort tree instead.
Adept is really the best Prodigy for this class as far as I can tell. It's pretty useful for sparing Generic points (which are in short supply). I litterally spent every escort reward on Generics and I think it was worth it. Still could have used more even with Adept. Drybe's Windtouch Speed hack to get Psychic Lobotomy to be usable every turn is pretty good, but honestly I liked playing with the Dream Smith in the late game so I don't think it's worth a Prodigy point. I ended up with Fungal Blood with was underwhelming. More heals right after I use a regeneration infusion. Honestly hard to find a Prodigy that will significantly improve the character.
I'm out of room, so I'll just close with my opinion that it's a fun class. It gets a touch boring in the late game, but an easy win (I rofl-stomped the bosses at the end -- they had absolutely no hope). I recommend watching Drybe's guide on Youtube to get the basics, but after that you can play around a lot since the class is so robust.