So I have just gotten past the first gym, and almost all of my Pokemon were knocked out in the process. I’m worried about future battles, and I’d appreciate any advice for my team.
First up, don’t feel bad about having your Pokemon knocked out during Gym Battles (and, later on, even during trainer battles), especially if you are running a 6-mon team early-mid game. Expect your Pokemon to be underlevelled relative to Gym Leaders and generally overpowered by the Gym Leaders’ superior movesets until they reach their final stages of evolution themselves (mid-game).
There is nothing wrong with your team, however you may want to consider diversifying your offensive typings. Your team notably lacks many solid offensive typings such as Rock, Ice, Psychic, Fairy, and Water, the inclusion of which could greatly expand your team’s neutral and super-effective coverage.
Given that you are currently doubling up on Ground-types, replacing Cubone or Nidoqueen might be an option (the former is slow and rather lacklustre until Thick Bone Marowak, while the latter you may find lacking late-game although gives you Fairy coverage). A solid replacement would be something like Huge Power Azumarill, which is a monster in all stages of the game and can compensate your team’s poor early-mid game.
Alternatively, you can switch things up and upgrade the likes of Blitzle and Ponyta, who are okay but have counterparts that are generally considered superior. Alternative Electric and Fire powerhouses in your stage of the game include Elekid or Magnemite and really most other early-game Fire types respectively.
You can also try looking up Friend Safari Pokemon for convenient upgrades to your team once you get your Secret Base. You can find a list of FS Pokemon and how to access them here.
You need an ice type either delta scyther or delta ralts. Azumarill with huge power might do it to tune the team a bit and go level 30 with a fire type and rest on level 25+. You will get delta scyther for a steel type on hut at route 3 and a delta ralts on hut at route 4. On the next town you get a secret base where you can access friend safari.