Nice choices.
You can make your images more screen-sized by adding in some width and height measurements.
150x200 is a good size for side-by-sides:
 
And if you want to do 3 across it’d be 100x133 each (though 100x130 is close enough, and easier to remember ). And 200x265 is a good size for a solo.
There’s also The Sandbox if you fancy a practice.