Hello Thapelo,
Glad to hear from you.
1. Yes, if you are trading with sideways indicators you aim at buying when the price is cheap and selling when the price is expensive. So yes, you better combine it with another sideways indicator or at least the rules of the indicators to be similar. It could be a Simple Moving Average but if the rule is to buy when it changes it direction downwards it becomes a sideways indicator, right?
2. Really hard to say which one is better. I have many strategies that perform fantastic with one entry rule. The idea is that when you use one indicator you will have more count of trades. When you combine a couple of sideways indicators, you will get the trades filtered and the trades will be less.
3. The indicators are the same for any asset.