Hi Roman,
Though I’m not entirely sure what you mean by a 35mm screen, the resolution of your sequence setting is something you can think of as your ‘top end’ resolution. When you’re done with your edits, you can export to pretty much any size you like. If you provide some more details about the project you’re working on that might be helpful to give more targeted guidance.
I think though what you’re describing is that your source video and stills are larger than the sequence. There’s an option called ‘Scale To Frame size’, which will automatically scale video frames down to fit within a particular sequence size. This is an option on a per-clip-in-timeline basis, and can be set to be the default in (win) Edit -> Preferences -> General -> Default scale to frame size (mac) Apple menu -> Preferences (etc).
You can also adjust the size / scale / rotation of a clip in the timeline when you have it selected in the timeline using the ‘Effect Controls’ window, or if you just click on it in the program montior, you get into ‘direct manipulation mode’ where you can see the size and scale handles as you would in Photoshop, etc.
Hope this helps.
-EricS