Some thoughts on balance and stuff that I had:
I love the selection of pokemon in the beginning and early game, but I think the main problem is lack of real viability for some starters. For example, Axew is really good as a starter, (see Rejuvenation) but Vanillite just kinda isn't, and both of these types would make for a very different starter experience. (Opinion alert) Really I found the best starters to be Axew and Litwick for the good movepool and base stats being solid. Zubat is probably the worst since you can grab another one immediately after the intro. But I'll go down the list for each type, starting with the top left corner:
-Happiny is a nice choice for a Normal type, but useless. Mud Bomb is a nice touch though. I would replace it with something like Lillipup, which evolves early like a normal starter pokemon and has good evolutions.
-Timburr for Fighting is pretty great, but trade evolutions won't pan out for starters unless we get a Link Stone from a main story section, or an obvious quest.
-Zubat was explained above and before in this thread; I would replace it with something that evolves by the first gym, like Spearow, Pikipek, or even something crazy like Oricorio.
-Abra works for Psychic perfectly, and I love that it starts with Knock Off.
-Litwick is good as a Ghost type starter because it has good moves to start with and access to Night Shade. Pokemon with guaranteed damage moves like Axew with Dragon Rage are always good. If we were to replace it (since it falls off pretty fast after 20, being saved by Flame Burst, but not really needed) I would put Drifloon, or Pumpkaboo/Phantump due to having an edge over the first gym and the surrounding area.
-Zorua is fine for Dark, though Nuzleaf could be fun.
-Roggenrola is a great Rock type
-Sandile is good; not many Ground types that are unique like it
-I love the Nidoran choice for Poison
-Klink is not the greatest choice for Steel, especially since it evolves so late. My alternative would be Magnemite, Alolan Sandshrew, or Beldum
-Yanma is a solid choice for Bug. There are others that I would prefer, but that's just opinion. wimpod plz
-Ponyta is a good Fire starter (pun absolutely intended)
-Axew is great because it's a Dragon type, but maybe Jangmo-o would be more fun. Or Deino if we hate the player and want to let them have a fully evolved starter
-Togepi rules Fairy pretty handedly once it's fully evolved; Ralts would be a good alternative since it's useful all the time
-Poliwhirl is alright at best; Tympole or Lotad would be better cuz Seismitoad is scary and Ludicolo is your new god. (Maybe Marill?)
-Electrike is great for Electric
-Budew works for Grass
I like the starters you chose well enough, but not all of them are useful. Moving on, the amount of battles in general is pretty good, I like the pacing of them in general, actually. The first gym is where we hit a wall. If you chose Axew, Electrike, or Timburr you should be fine since you can get a good carry going on, but even then, 6 pokemon with several knowing Scald and opening with a Black Sludge Tentacool that also knows Scald is a bit much. I would consider scaling that back a bit, except for Gyarados. That's pretty good as a closer 'mon. Maybe keep the Tentacool with Scald, or the Sludge, but not both.
The selection of pokemon everywhere is pretty nice, and you can get a decent team pretty quick. I liked finding a Misdreavus and Dusclops alongside my Litwick. I would say throw in something that can work with the gym like a decent grassy pokemon or swap Electrike for Blitzle or Tynamo and put it somewhere relatively rare. Also, I love the idea for HM stuff; never made sense why my pokemon that can punch through a wall can't break a rock.
I am definitely looking forward to the upcoming stuff and where the story goes, cheers!