Architecture advice

Hello forum!

We are in the early days of an initiative where we, as the parent organisation, want to create a sort of ‘franchise’ model where ‘child’ organisations sign up to our parent not-for-profit and are offered a pre-developed WordPress website structure for ongoing development. This would include template/security/plugins. The environment is Local Stories so independent organisations will be sourcing news/events/information in their region. They will have their own URL eg. myorganisationnewyork.org, myorganisationseattle.org etc.

What is the best structural arrangement for 100+ sites (and potentially 500)? If all the sites are sitting on one server (multisite) and one site is compromised and the hosting account suspended, the whole 100+ falls over but if each site has its own hosting, one falling over will not affect the others.

Pretend for the sake of the question that cost isn’t an issue because we recurring expenses (eg. Wordfence, template etc. etc. are about $200 p.a. and these costs are part of the child organisation’s annual running costs). We aren’t influenced by cost, we’re influenced by building a bullet-proof structure.