Where can I store the data from my customers?

Hi,

I only use zoho email, contact list and invoices, but those three contain quite a lot of information about my customers. I don't have a payment system installed, as everything is paid to me by bank transfer, so that is not a concern. My main questions are:

- Can I still keep all the emails and the info about my customers on my contact lists (I provide activities to children, so there may be details about the names of the parents and children and area where they live, but not full addresses there). I usually keep this as a reminder of how the customer reacted (good or bad) and it's good to have some history, in case I decide to have someone else taking over the business and knowing all this useful info.

- If there is something I am not allowed to keep, where can I storage it to be considered safe? In a folder in my computer ? (may be stolen ), in the cloud? (may be hacked). Where should it be kept to be considered safe? Does zoho provides a system to keep it safe or do I have to buy it from a third party?

- If one of my customers asked me to see what kind of info do I keep about them, how can I show them? Do I have to search all the emails or is there another way, like a checklist that zoho has where I can show them, saying : item 1, yes, item 2 does not apply, item 3, yes etc...

- Is it really true that they have to opt-in so that I can keep them on mailing list? What about everyone that registered before to my newsletter and may not see that on time? I know they can subscribe again later but most of them will not remember to do that.

I know the deadline is on the 25th but is there an extra period of time, so that businesses can still contact previous customers, to make sure they don't t forget to click the button and opt-in? I am very concerned that I will lose most of my customers, and am not sure what to do if they don't click that button...

Thank you,