Is increasing gas fee for BTC the only way to speed up its transaction speed? Also how can one use a lightening network in a BTC wallet? I've heard about this but I don't know so much about it..
Apart from Bitcoin is it fine to add other coins as a means of payment in your local business? Is this fine or it's better to stay with Bitcoin only.
You just raised a topic of concern as regards transaction fee. This is what most people do not understand. Some are yet to get it clear how transaction fee works and why does most transactions take much time to scale through.
As you have said that is how it works. The higher the transaction fee, the faster the transaction scales through. It depends on the fee request from your application from which you are carrying out the transaction but if you want to set the fee in the higher side for your transaction to speed up very fast it is your decision and will to do so.
The issue of adding other networks to your acceptable means of of payment is up to you. But if you are choosing, note that bitcoin has a strong base compared to others and also the most popular amongst other coin you hear about. There are other stable coin out there but for me, I will prefer to go with bitcoin as my own means of accepting payment for services rendered.
You can as well check the above Link as being posted by the other poster to know more on the lightning network.