Managing a Car Club Membership

I am wanting to evaluate CB Subs for my Car Club to manage our members annual and life membership subscriptions through an existing Joomla website that does not yet have CB installed. This Joomla site is currently only used with Acymailing to distribute a monthly newsletter to about 160 email addresses. Most of those email addresses are not currently registered on the site as Joomla users, only for Acymailing.
I have gotten a bit lost/overwhelmed when trying the CB Subs demo site and have some questions.
1. When purchasing CB Subs is it also necessary to purchase a Developer or Professional Joomlapolis subscription or is it included with CB Subs?
2. To use CB Quickstart to install CB Core and CB Subs should it be be installed to a blank site or is it Ok to install on the existing site?
3. When CB Core and then CB Subs installs, will they linkup to the existing Joomla and Acymailing subscribers or is there a manual procedure to make this link?
4. On the CB Subs billing side, our financial year finishes on 30 June and part year pro-rata memberships are charged. Will CB Subs work out the correct charge and be able to handle this when the subscriber joins?
5. On exceptional occasions we grant (annual) membership in excess of 12 months. Is it possible in CB Subs for someone (Administrator?) to override/change the 30 June expiry date to grant an extension to the 30 June in the following year?
Thank you for your time.

1. When purchasing CB Subs is it also necessary to purchase a Developer or Professional Joomlapolis subscription or is it included with CB Subs?

The Developer membership includes CB Paid Subscriptions. The Professional membership does not. If you purchase CB Paid Subscriptions individually then that's all you'll receive. Our memberships table below details what's included with our memberships.

www.joomlapolis.com/memberships

2. To use CB Quickstart to install CB Core and CB Subs should it be be installed to a blank site or is it Ok to install on the existing site?

It's ok to install it on an existing site, but it's not really its intended design. CB Quickstart was primarily developed with the goal of quickstarting a fresh site into a social media site.

3. When CB Core and then CB Subs installs, will they linkup to the existing Joomla and Acymailing subscribers or is there a manual procedure to make this link?

CB will automatically synchronize your Joomla users on install. Nothing is necessary in regards to AcyMailing and will work as expected.

4. On the CB Subs billing side, our financial year finishes on 30 June and part year pro-rata memberships are charged. Will CB Subs work out the correct charge and be able to handle this when the subscriber joins?

CBSubs supports "By Calendar Year" duration. This provides yearly subscriptions locked to calendar years. With it you can specify the year start month and day. So that should work for your current situation.

5. On exceptional occasions we grant (annual) membership in excess of 12 months. Is it possible in CB Subs for someone (Administrator?) to override/change the 30 June expiry date to grant an extension to the 30 June in the following year?

It's possibly to modify subscriptions manually by administrator, but is generally not recommended. If it's a recurring subscription then you absolutely cannot modify it. There's no functionality for buying additional time for an existing subscription beyond just renewing the subscription. So the answer to your question kind of depends on if you're going to use auto recurring payments or not.