There are just two approaches to your community planning.
1) The Objective-based approach. You have a fixed outcome and work backwards to achieve that outcome. i.e. to achieve {X} I need {X} number of members. Therefore I need to send {X} invites and engage in {X} activities. Everything is planned and measured on a strict schedule.
2) The emergent approach. You launch with a few people, then see how the community develops, grows and adapts. You stimulate activities and let the community expand at its’ own pace. It doesn’t matter how fast the community develops, it matters how well it develops.
The objective-based approach should be properly measured and planned out beforehand. The emergent approach shouldn’t. The objective approach has a fixed target number of members, the emergent approach does not.
If you want unlimited members you can’t use fixed strategies and tight measurements to reach there.
This is where the problem lies. The same organizations that want unlimited members also want rigid strategies. Sorry, but it doesn’t work that way. Pick which approach you need (hint, option 1 for short-term, option 2 for long-term) and stick with it.