What niche?
What price point?
What are you offering?
What is your CPL target?

Figure it out backwards:

40 leads = 5% conversion rate
40*20 = 800 opt ins per week (at least) at a 5% conversion rate
800*20 = 16,000 clicks from campaign.

At a $1 per click average, you would need to be able to spend 16k per week on your advertising.

I think your numbers are too aggressive, especially if you are posting this as a general question here on Clarity.

How do I know this? This is what I, and my agency do.

We can have a conversation, and I can provide some more direction for you, but in general I would look at getting 1 lead per week at first, and then scale from there.