The first question has to do with the financial cost
This depends on the blockchain. For Sol is it very cheap. You can do it through various websites and they will charge you 0.05 Sol to crete the token + a service fee of around 0.15 depending on what site you use. You can also skip the step of doing it through a site and create the token yourself in terminal and it will cost you just the 0.05
For Eth it can be more complicated because there are a lot more options when it comes to code a lot more functions when compared to Sol. The more complex the code the more in gas fees you will pay when deploying it. Simple token you can launch for maybe 0.10 Eth and around 0.3 Eth for one with more functions. There is a lot of nuance.
Now that's just the token setup, next you have to setup the liquidity pool (LP). This is completely up to you how much you put in but it will determine if investors will be interested in the token or not. Not too much and not too little. For the LP you will also pay gas fees. For Sol Raydium will charge you 0.2 Sol for the cheapest LP option and for Eth Uniswap around 0.05 Eth
After that you have your community and marketing expenses but I wont go into that here
Also recommend leaving some amount to buy your coin to encourage other buyers.
Some like to allocate tokens to themselves as the team at launch. Some like to stealth buy at launch. Some like to create fake volume for their coin. Again this depends on your stategy and overall goals of the project.
Others say that in the first seconds after listing a coin is bought by robots and you can make money on it if you sell everything at that moment.
Depending on what functions your smart contract has it can get snipers or not. Because some functions could be dangerous to buyers and those coins dont get sniped. For example coins with a blacklist function dont get sniped
When you as the dev sells you will create FUD. Thats why some like to stealth buy. This is really up to you but you don't want to create big red candles on your chart again that will create FUD
Sell for another cryptocurrency, I take it?
On Eth you sell your token for Eth and on Sol for Sol. You could create other LPs with other crypto pairs but for small coins that is not needed.
What about the rest of the coins that someone else bought? Put a buy/sell commission on them?
Sol is very strict when making the smart contract, you either apply trading fees at the start or not. There is no applying fees later on with Sol. For Eth this is more flexible as I mentioned, you can have no fees at the start and then later change that as you need. Although keep in mind that this can raise some red flags for investors.
Then what's the point of all these memcoins?
Its only gambling and greed dont try to find a deeper meaning behind all of this
Hope this helps