Offer free WiFi

I help run a volunteer tourist information office and we would like to offer free WiFi. We have Zen FTTC and could use a router with two WiFi signals, one secured for us - one open for visitors.

However, I think we have to be able to identify who is using our WiFi.
Is that right? Do other people do it? and how?

Thanks for all clarification and suggestions.

I don't think you'll find you have to identify people - you can offer public wifi without knowing who specifically is using it (like many pubs, coffee shops, libraries, etc do).

But, you will need to check with Zen that you are allowed to offer this under your Ts&Cs.