I have dumb questions, please entertain them and explain to me why my idea is good or bad, thanks!

I have dumb questions, please entertain them and explain to me why my idea is good or bad, thanks!

I have a regular brokerage account just FYI. Let's say I find a stock I like at $100 that I think will go up. Are there any negatives aside from losing some money to buy it at $100 and immediately put a sell order for $99. If it goes up, I make money. If it goes down, I lose $1. During day trading, I get it, but if the market crashes overnight I am assuming I get destroyed and it may sell for lower than my sell order of $99? Is a sell-limit order going to help me even in this scenario?

Second question is, let’s say same scenario I want to put a limit order for buying a stock once it his $100, can I also have a sell order WITHOUT OWNING a stock to sell at $99? Or I have to first own it?

Also any tax repercussions for this type of transaction if selling at loss?

Thanks!