Just on the timeline- as
@Ja***
said, it takes around 4 weeks to get approval.
You pay nothing before this process- so you can start it now and you'll likely be approved in four weeks. You get a letter of approval at that point.
That letter is then valid for three months. You can put off actually paying for those three months, but basically as soon as you pay (within a few days) your membership will be activated and you can get the visa.
This is just to say- you can start the process now, you don't have to pay right now, you won't need to hand over money for at least a month and you can string out your approval letter for even a further three months after you get that, if you are not sure about it.
Personally, I think I'd want to be 100% sure it was getting me in before actually paying.