I wouldn't get your hopes up on the OCVs. The numbers will be fudged and my suspicions are, much like many other people, that the intention was the design the requirement around the AUSTAL MRVs. Not much of a blue water vessel but a useful Armidale replacement..
Austal has changed its site, but the origional MRV Austal had in mind was about 1000t (simular to the multirole corvette). the WP 2,000t puts it right in the LCS range, which I think was a bit more than most people were expecting. Austal would be a front runner with its LCS experience(having built the Armidales as well).
While these won't be perfect blue water ships, they will certainly be capable of blue water activities with greater size, equipment and range while still being excellent ships for non-open water operations.
I think we will see the OCV end up looking fairly simular to the LCS. However, I would imagine systems like 50 cal, CIWS (Phalax/Searam), mini typhoons/typhoon, some sort of small missile system (RBS-70/starstreak based?) or possibly up to harpoons etc might be shared from a pool. This pool can be enlarged fairly easily given 6-12 months notice.
The OCV will end up replacing almost everything. Armidales are an obivious replacement (14 boats), Huon class (6) and possibly survey vessels Paluma class (4) boats and leeuwin class (2) boats.
But there are a great deal of not very old boats. I'm not sure what they are planning to do, sell them off (NZ, Indonesia, Malaysia, Arab states), give some away (to say pacific island nations to strengthen their "navies", PNG this has become a increasingly important issue as they are unable to secure their EEZ), deactivate or keep them as training vessels to increase numbers of RAN personel.
20 OCV's would be totally impressive. We would then have enough vessels to really operate a fleet and a task force operations on our lonesome.