I'm not an expert, but I will share my experience here.
1. On any one exchange, I check the Sell and Buy Order books. My first question here is, these sell and buy order books move so fast that it is difficult to look at them and analyze in real time. Is there another way to do it? The rows keep moving up and down as and when the orders get executed.
Don't depend on the order book only. Every traders can remove their order and there is a trading bot that playing on the market too.
3. I see a few big sell orders at a certain price X which is Y% greater than the current price. Does that indicate a high resistance level at the price X? Can I expect the market to go down once it reaches the price X if there are a lot of sell orders at that price? Is there a better way to analyze?
These sell order can be removed anytime, watching the platform to see the price movement is require much time and it's not guarantee if the sell order will be execute.
I think it's better to look back at the last resistance line, if it match with these sell order it's possibly that indicate a high resistance level.
you are overthinking it. looking at orderbook "depth" (which is the chart that looks like a V where the buys and sells merge in the middle) is just an analysis so that you can add another reason for making certain trading decisions. for example you want to buy expecting a price rise then you place a couple of buy orders around the support level (a big chunk above, small chunk higher above, small chunk below and another smaller way below the support).
nothing in trading is guaranteed, so you just analyze to the best of your abilities and make a move based on changing market conditions and change those decisions with the sudden changes.