I am a long time photoshop user. Started with PS6, moved to CS2, Then onto Adobe CC photographers plan as well as the illustrator cc plan.
The minute i saw that Affinity photo was available for windows I jumped on it and have not looked back. Despite taking a small financial hit, I have cancelled and unsubscribed to all adobe products.
As far as the nik collection, there are several videos and tutorials showing how to get them into Affinity. Once you do, they are available through the filters menu.
The Affinity UI is very similar to PS and illustrator. The icons may look a bit different, but the keystrokes and layout are very similar. It didn't take very long to get it down.
I've still got an older copy of LR installed because I like the print module, and it works very well with my Epson 3880. However, i'm experimenting printing through AP and am very happy with the results. As with any change, it just takes a little time to get used to.