You can customize keyboard shortcuts in the preferences.
You can convert any shape into a picture frame by selecting the shape and using Layer > Convert to Picture Frame. And you can use the clipping option known from Photo and Designer.
https://forum.affinity.serif.com/index.php?/topic/4069-layer-clipping-vs-layer-masking/&tab=comments#comment-16825
So far I'm really enjoying Publisher... you guys are doing a great job! The only feedback I have for you is little things that I hope are coming in future betas :
• "Place" needs a keyboard shortcut. I keep wanting to hit Cmd-D or something and realizing I have to go to the menu is a little slow
• No way to specify # of pages in new document window.
• No way to place images into custom shapes. I realized I could emulate a circle by changing radius... but any other shape seems impossible.
• Export persona.Publisher seems like it could really use an export Persona, which works so well in Photo and Designer. This would allow for packaging files, including fonts, graphics and instructions into a folder structure that can be zipped and emailed off.
Again this is a great complement to Photo and Designer! I'm looking forward to the final release.