If money wasn't a concern it would be very easy to add numbers but I was trying to be realistic with my numbers. Having the four platforms should ensure two of each at any given time at least for the first 10 years.
A very large issue with the idea though, is that the numbers are not realistic. If you want to reliably have two examples of platform
x available or on operations at any given time, that would typically require a total of six or more of platform
x in inventory.
Pretty much the only way to possibly maintain a 50% availability/deployment rate for a platform would be to have a very low operational tempo for it. For something as useful as airlift, a force would not deliberately keep the tempo low, unless something was wrong with the platform.
When considering aircraft numbers, look at the RAN's MH-60R 'Romeo' naval helicopter acquisition. The programme service requirement was for there to be 8 naval helicopters available for or on operations at a given time. In order to meet that requirement for 8, a total of 24 MH-60R 'Romeos' were ordered.
Having a total inventory of 8 across two different platforms, would normally mean that a single example of each platform is either available for use or already in use/on a deployment. In addition, about two-thirds the time, an additional platform would be again either available or already on a deployment. However, that additional platform could be of either design, and due to limited numbers it could not be reliably be the same (out of the two) design consistently available.
IMO it would be better to dedicate more resources to having a greater number of larger and longer-ranged transports, than having a split airlift fleet with such a small pool of platforms. Even if the RNZAF does go with the C-130J as their 'big' transport (which IMO is too small absent a larger RNZAF transport also in service) then it would be better to get six or more, and skip getting a short-haul transport. A C-130J can airlift a small cargo & personnel over a short distance like the C-295 can, albeit not necessarily as efficiently or cost-effectively. However, a C-295 cannot take the place of a C-130J to airlift a cargo over a long range, especially if the cargo has a high volume and/or displacement.
It would be nice if the RNZAF could build up a split air transport fleet with sufficient platform numbers to provide useful service. This might even be possible with a NZD$20 bil. CAPEX spend. Trying to be efficient by splitting the fleet and only getting a small number of different sized platforms will IMO turn out to be "penny-wise, pound foolish" at best.
It is also worth noting that while smaller transports do cost less to acquire than larger ones, it is not necessarily by a huge amount. A C-130J has a unit cost around USD$73 mil. in 2016 dollars. A USCG HC-144 Ocean Sentry, which is the FITS-kitted version of the CN-235MP, which can swing between SAR, maritime patrol/surveillance, and air transport roles, costs ~USD$30 mil. for just the airframe, and a total of ~USD$50 mil. per aircraft once the cost of the modular control stations for the maritime patrol roles are factored in. I am not aware of an in-service version of the larger C-295 which also can/has a swing-role capability, otherwise I would examine the costings for that. It does suggest though that adding in the ability to go from being a pure transport, to a non-transport role like MP, SAR, water-bomber, etc. does significantly increase the acquisition price
The last point I will make right now, for people to consider is the degree of importance short/light tactical airlift has to the RNZAF and NZDF as a whole. The last Andovers were withdrawn from RNZAF service (June 1998) almost 20 years ago having been configured for VIP and utility transport roles. Since that time, Beech King Airs have been leased to provide some VIP, transport and multi-engine training (in place of the F27 Friendships). However there has not apparently been sufficient need/importance for a replacement like there has been for the larger RNZAF airlifters like the C-130, B727, and now B757. Given the apparent overall lack of interest, I would suspect that air transport will first focus on covering the most important service needs first.
If resources remain after seeing to that, then we might again see light/medium tactical airlift in RNZAF service.