I always recommend Paypal as an option for a few reasons:
- Many people don't like using their credit/debit cards online
- Many people prefer Paypal for online purchases and won't use anything else
- Paypal's buyer protection is fairly good in the case of disputes
To answer your questions:
- How many people use PayPal
A quick web search suggests over 230 million
- PayPal demographic - do older customers use it?
- Does conversion rate improve with PayPal? If so, by how much and what is the research to back this up
I've seen conversions improve by 25% in some sites, no specific research but what I've found building ecommerce sites over the years
- Cons to PayPal - for instance, will we have the customer data?
You'll have things like name + shipping address (which is all you need), plus whatever extra data is required to fulfill the order.