Assets/images issues - no thumbnails showing in Perch? Also, not cropping

Trying to understand what's changed (and what I need to change), when using the new assets feature - I have a bevy of questions:

1. When adding an image into assets, Perch asks for; Title, File & Tags. When I do this, it tells me the asset was successfully created, but there is no sign of the image (which I assumed would show as a thumbnail like an uploaded image used to before 2.5). Is this correct?
2. Returning to the main assets page shows the file, but only with a gray icon denoting an image file, not a thumbnail of the actual image itself. Is this also correct?
3. Uploading an image via a template (from my previous site running 2.4.9), now gives a link asking "Select or upload and image". This presents me with a slide-out assets panel, with the gray 'image' icons to select from, or add an asset. The 'add' panel instantly vanishes the moment a file selected for upload (there's a brief flash of a progress icon as everything disappears). This file is never seen again. Once, before clicking on save changes, I was shown an image dialog box (where I used to see a thumbnail in 2.4.9), but this had no thumbnail displayed, just some basic info about the file and the option to remove it. I've never seen this again - instead, I'm presented with the "Select or upload..." option, as though I haven't selected any images. However, while the image is never visible from within Perch, it usually shows up ok on the website - but always in its original resolution - never cropped as specified in the template.

I'm obviously doing something horribly wrong here. The only change I've made to my previously successful template is to add bucket attributes to the images. The image files I'm uploading are all well under 1MB. As of today, I'm running 2.5.2.