CandyCotton

I think you can get Meltan Candy from doing the quiz on Discord, saving up coins and eventually buying it but I don't know how much it is. Judging by the amounts people put it up for, you might have to grind a bit to get some (you need 50 or something to evolve Meltan). I'm not entirely too sure on that though.
 
Your other option would be Pokebay and even though it's a lot of money, there are ways to grind and get the money required, such as catching a team of level 6 Pokemon with an immunity to another type (catching a ghost type for example because theyre immune to normal) and using a training account.

Short answer: To have the ability for legendaries to spawn in the world, you only have to beat the gyms, not the elite four and champion (but you can still do them nonetheless).
 
Long Answer:As you may or may not have noticed, if you go on your profile, at the bottom of the page there are something called "Legendary Pokemon Unlocks" and each ribbon unlocked means you can encounter legendaries native to that region. For example, if you only have the Kanto Ribbon unlocked, you can only encounter Moltres, Zapdos, Articuno, Mew and Mewtwo in the world. If you also unlock the Johto Ribbon, you can encounter all the Kanto legendaries and also the Johto ones, and so on. (I think Mythicals are unlocked this way as well)
To unlock a specific ribbon, you have to defeat the gyms associated with that ribbon's region. If you want to unlock the Kanto Ribbon, you have to fight and win all eight gym badges for that region. You can fight all Kanto-Alola (Alola does not have gyms but it does have Trial Captains and Kahunas, and you need to defeat them all to get the badge) gyms by going to Battle->Battle in a Gym->then use the headers provided to fight. To access the Galar gyms you have to find them on the map, rather than using the menu.
After doing that its just a matter of getting lucky and finding a legendary in the world since they're pretty rare.
 
I hope this helps and I am more than happy to provide you with more information if needed!
 

The cheapest and most guaranteed way to get a mega stone is by buying them via the Pokemart, however they only sell Mega Stones for starters. You can buy them off PokeBay, but they will most likely be much more expensive due to its rarity/ difficulty to get. Getting them off Sidequests is a good idea but it can take a while.
 
To get money faster you can use training accounts, go on Pokemon Vortex every day (because sometimes you get PDs as a daily login prize) or you can offer your Pokemon in return for PDs (again, not the best way but if done efficiently can be useful)

If you mean leveling up you can use different training accounts (you can go on Google and look it up).
If you want money/ PDs you can catch a load of lv6 ghost Pokemon and use the training account trainingghost 
For friendship just battle a load of wild Pokemon i guess

I don't really know how to explain it but i'll try.
The way I make the emojis bigger is by using the icon shaped like a Pokeball (near the Balbasaur) when making a message. When you click or tap the Pokeball it says "Pokemon name". Put the name of the Pokemon you want in there and if you spell it right, the image of it will come up. If not, it will show the spelling of how you spelt it with a green icon thing like this- . If you do it right you'll get something like this-  
If you want a mega form, simply put mega after the name eg "Garchomp (Mega)". For shiny or shadow or other varients put that before the name of the Pokemon eg Shiny Pikachu.
This is just how I do it anyway.
 

I don't really know how to explain it but i'll try.
The way I make the emojis bigger is by using the icon shaped like a Pokeball (near the Balbasaur) when making a message. When you click or tap the Pokeball it says "Pokemon name". Put the name of the Pokemon you want in there and if you spell it right, the image of it will come up. If not, it will show the spelling of how you spelt it with a green icon thing like this- . If you do it right you'll get something like this-  
If you want a mega form, simply put mega after the name eg "Garchomp (Mega)". For shiny or shadow or other varients put that before the name of the Pokemon eg Shiny Pikachu.
This is just how I do it anyway.