Hi Sandra,
Thanks for reaching out.
Columns inside a Collection — Row and Columns can't go inside the Collection addon, but the Div addon can. Drop a Div in, set Display to Flex or Grid (Div → General → Display), and nest more Divs inside it holding your Dynamic Text / Dynamic Media addons. That gives you the grid from your screenshot, repeated per item.
The Collection addon also has its own: General → Layout → Type (Grid or Stack), Columns, Column Gap, Row Gap, each with a per-device setting.
For one project across a full page, use a Detail Page: Pages → + Add → New Dynamic Content Page → your collection → Detail Page. There you build with normal Rows and Columns and the dynamic addons map straight to your fields — no Collection addon needed. Keep the Collection addon on your listing page for the project cards.
Laptop vs mobile/tablet — one template is enough. Rows, columns, Divs and addons all have per-device settings, plus Advanced → Responsive → Hidden on Laptop / Tablet Landscape / Tablet Portrait / Mobile Landscape / Mobile Portrait. Content is entered once in the collection item either way.
Slideshow — yes, this works. Add a Gallery field to your collection, then use the Dynamic Media addon and turn on Enable Slider (General → Options). You get width, height, gap and radius controls, and the images stay per-project.
Colour patches — there's no Color field type yet, so a hex value can't drive the CSS. Use an Image field with a small solid-colour image per shade and output it with Dynamic Media.
Hope this helps!