I am gradually moving across to mirrorless. I got the Z6ii. It came with a 24-70F4. In my view it is not a good choice for birding. Few things are. My D500 has been good. What I really found was how good the new Z-mount lenses are. I have kept my longer F-mount lenses (300 &500).
For birding I blew the budget and bought a Z9. It was out of my price range - and then I realised I had never owned a flagship camera because they were too limiting. The Z9 is amazing. I have been buying a few Z lenses and eventually all my F mount short lenses (200 or less) will be gone as will my DSLRs.
In my view mirrorless full frame is on the one hand too expensive and at the same time well worth it. Too expensive because it means you will find yourself replacing most of your stuff! Well worth it because it opens up goals and opportunities you never thought you could reach for. I quickly realised that it challenged lots of my assumptions. I have shots I have taken at 1/30,000th of a second for example but it is the lack of vibration on the Z9 shutter that surprised me most. I am starting to explore night time photography, often without a tripod and it turns out I have been able to hand hold shots at 1/15th of a second.
I think you should buy the Z7 and start to explore what it offers.
For birding I blew the budget and bought a Z9. It was out of my price range - and then I realised I had never owned a flagship camera because they were too limiting. The Z9 is amazing. I have been buying a few Z lenses and eventually all my F mount short lenses (200 or less) will be gone as will my DSLRs.
In my view mirrorless full frame is on the one hand too expensive and at the same time well worth it. Too expensive because it means you will find yourself replacing most of your stuff! Well worth it because it opens up goals and opportunities you never thought you could reach for. I quickly realised that it challenged lots of my assumptions. I have shots I have taken at 1/30,000th of a second for example but it is the lack of vibration on the Z9 shutter that surprised me most. I am starting to explore night time photography, often without a tripod and it turns out I have been able to hand hold shots at 1/15th of a second.
I think you should buy the Z7 and start to explore what it offers.