Not a 9mm specific upper, just a regular forged upper, with 9mm components installed obviously.

Yes

The bolt carrier needs to be shaped right to not smack into the feed lips on glock magazines.  The receiver will work fine, but if you were talking about using an existing "complete upper" that you had, your bolt carrier might not be plug and play.

By hybrid, do you mean PSA's hybrid BCG, or any 9mm BCG that is cut for Glock mags?

Not entirely true.  I run a PSA forged Glock lower with the LRBHO lever on it, which has worked everytime.  I use an NFA modular bolt.

Yes, Any 9mm Bolt that is cut for Glock Magazines, I'm using the Spinta Precision 9mm Bolt in my 9mm AR, They have some good deals on Blemished Bolts, Also the KVP Bolt, and PSA Hybrid will work fine.

PSA uses the term hybrid to indicate their bolt will work with either Colt or Glock lowers...found that little tidbit on their website.  I'm running a PSA Glock lower with a TACCOM bolt. Runs like a champ.  I'm very pleased with the combination - so far. I think any upper will work...I'm using a Anderson.

Agree with comments above: my understanding is that the PSA "hybrid" upper is really just talking about their bolt that comes with it.  I can't speak for others, but my actual upper receiver is a standard mil-spec receiver with the brass deflector and forward assist- not my first choice but when dealing with PSA some times you have to take what they have in stock and on sale with free shipping. I've come to like it's looks ok and have not had any issues with it and the glock billet lower (no bolt hold open but may try the NFA upper at some point...(I think that was the one that might work with it) - but it's really just a fun gun to shoot cheaper than 556 so no rush to change things for me.

PSA's "Hybrid" Bolt is actually a New Frontier Armory 9mm Bolt, "Hybrid" refers to being both Colt and Glock Magazine capable. Any 9mm Bolt will work as long as it is cut for Glock Magazines, The only 9mm bolt that I have found that will not work with a Glock Magazine lower is the CMMG, it is only cut for Colt magazines, Any AR upper receiver will work, Bolt assist or no Bolt assist, Door or no door, All you need is a Glock Magazine Lower, 9mm Barrel, 9mm (Glock Cut) Bolt, 5.5oz or heavier Buffer and your ready to go. Then choose your Carbine length Buffer tube and Handguard. Go to the Pistol Caliber Picture thread and you will see a myriad of options. PSA also has a habit of stating that their Bolts, Lowers , Barrels and other items  only work with their products, a Marketing ploy to get you to buy more of their stuff.

I'm not a PSA Basher, Both of my 9mm Lowers are PSA and I buy a lot of stuff from them.

PSA has a sale on "Their" 9mm forged lower, Spinta usually has a good deal on Blemished 9mm Bolts, KAK and KVP also run deals on 9mm Blemished barrels, If you shop around, You can put together a nice 9mm Pistol or Carbine for a reasonable price.

Palmetto State Armory makes both Colt pattern and Glock pattern dedicated lowers that are good quality.

I have their dedicated forged Colt pattern lower.  A friend has their dedicated billet Glock pattern lower.  Both have LRBHO built into the lower.

^ this and you don't even need special "9mm" parts (other than barrel and bolt of course)- mine works fine with a standard A3/M4 style flat top upper.

this is 100% true for me too... Went to order a slick side upper, no longer available... waited a few days and the standard one was there with barrel length and hand guard I liked so I got it before it went out of stock also.  I have since learned to just like it the way it is and have not had any issues with feeding or ejecting etc.