not necessarily. Please have a look at http://www.dongleauth.info/ Every site which supports OTP should be able to make use of the NK Pro and Storage. There may are sites which does only support U2F. In this case you can not use the Pro or Storage for authentication, but only the FIDO U2F.
We will update the shop-page as soon as we know a precise date. Shipping should be done in autumn.
It may depend on the actual use case. You can use the same pgp keys/subkeys of one NK for different keys. I plan to write a new instructions for this. Until then this site is the most detailed and complete resource. So everything you use the pgp keys for, can be managed with different nitrokeys. OTP and other secrets are mostly bound to the card itself.