Welcome back to Pokémon!
Should I start at the beginning with Gen 1 does it make much difference?
You do not need to start in the beginning! Pokémon is generally a pick up any game, any time, and get whole new experiences while still being familiar. They do not follow a linear storyline, with the biggest exception being Black2/White2 being direct sequels from Black and White, although you do not need to play them in order to have an enjoyable experience.
My advice for picking out which games you want to play should start primarily with what games you have access to. In modern times, games for the Nintendo Switch are the most accessible. Mainline games for the Switch are Let's Go Eevee and Pikachu (Gen 7), Sword and Shield, Brilliant Diamond and Shining Pearl, Legends Arceus (Gen 8), and Scarlet and Violet (Gen 9). There's a lot of spin-off games as well, but it's generally recommended you start with a mainline game. Lets Go Pikachu and Eevee are reimagined versions of Pokemon Yellow -- one of the first Pokemon Games. If you're looking for modernized nostalgia, they're the way to go, although one of the biggest critics of those games being lack of content, and being too easy.
If accessibility to games isn't a concern for you, fan favourites are typically considered to be Emerald, Platinum, HeartGold/SoulSilver, and Black/White. Check here for a complete list of games.
Each game comes with their own pros and cons, and no game is perfect. I'd highly recommend looking into options and seeing which suits your taste the most! Watch some videos, read some opinions. Just note that mechanics change in between generations, so it may be a little overwhelming jumping huge gaps forwards and backwards. I'm happy to give you a detailed breakdown of games pros and cons if you need!
Do Pokemon stats, evolutions and Movesets change in different Generations do I need to read up on patch notes?
Yes, there's a lot of changes in between generations! There's no need to read up on sort of patch notes, though. If you wanted to know Pikachu's moveset in Emerald, you just go to Pikachu's Page, and press "Gen III" under learnset.
I highly recommend Bulbapedia's Walkthrough Series, as it provides comprehensive gameplay guides for the game you're playing. It'll have everything you need to know about the games you're playing. Anything that isn't covered, you ask here ;)
Is there a game or 3rd party to battle other players?
Yes! Pokemon Showdown! is the most popular place to battle other players in real time. There's also spin-off games that focus around battling NPCs, and post-game features in some games have sections dedicated to battling NPCs. You can also battle people in Sword/Shield and Scarlet/Violet.
Is using non damaging movesets worth using in the game story or only useful against real players in battles?
They can be useful in-game, it depends on the move and circumstance. Normally you can brute-force just about anything, but sometimes it helps to raise your attack all the way to sweep the other trainer's team in one hit. Try things out, and come up with your own method of battling!
Any Tips and Advice would be nice
Watch videos, and ask questions!!! Approach everything with an open mind. Don't be afraid to try things. For challenge runs, make sure you've played the game first so that you know what to expect and don't get frustrated. It helps to learn from people, do watch popular PokeGameplayTubers if that's something that would interest you. That way, you can see how the games are, that moves do what, where to find things, and more. I personally watch and learn a lot from Smallant as he pushes games to their limits.
We have a great community. While chat isn't always active, if you ask a question there, someone will respond to you in under a day, either there or on your wall. Don't be afraid to reach out!
