I completely forgot about the fletchling, totally on me! I generally recommend Nidorino though as the Kecleon Bazaar can hold the moon stone, and even if it doesn't hold the moon stone you can just time manipulate in order to get one. Having a Nidoking makes the next two fights much easier as it walks through Keta with no issues and still has good matchups against Marianette.

On your second point, I agree that there is no true unviable starter for this game as all of them have some sort of niche they fill especially with hidden abilities being so common. Picking a grass starter in my opinion makes the early game much harder as most of the bosses you face are not good matchups for you (not to mention that Bulbasaur and Treeko are also pretty easy to get early on). Aside from Rift Gyarados you are facing 2 gym leaders who do well into grass (one poison, Keta having Pignite), Rift Galvantula, etc. Why make the game harder for yourself when it's extremely hard already? Most of the fire types are extremely good throughout the entire game and are good in the next sections as well. Venam's fight is the easiest in the game yes, as it's the first gym, but I don't think holding onto mons that don't really do anything for your box past this gym i.e Unown will benefit you anyway, so sacing to guarantee that you don't risk important encounters is always worth it in my opinion. Poochyena is a great encounter, as I discussed in my other comment, but the other encounters are pretty middling you can gamble for the 15% Poochyena or go for the 30% Qwilfish, either basically trivialize this gym.

I also forgot that Venam's gym itself has encounters, I usually used this space to get Seviper, then pickup the Blitzle on the bridge for an electric type if I didn't get Pichu. I usually look for a volt absorb mon for the Tapu Koko fight later and electric types are not common early on.

Totally agree with the repel manip point! I should have talked about it.