Unfortunately the playback rate of the VSE is not it's strongest side, however there are a few things you could try to optimize performance:
Select your clip and in the Sidebar make sure that Blend Mode is set to Cross.
Still with the clip selected in the Menus select Strip > Add > Movie > Set Render Resolution
In the View menu, switch Show Cache off.
If none of this improves the rate enough, then add your clips to a folder, and use the Velvet Revolver add-on https://github.com/tin2tin/blender_velvets/blob/master/Blender_2.80/velvet_revolver.py to batch generate proxy files, and then use it for switching between proxy and intermediate files.
Try first to generate proxies which are the same size as your original files, but using the h.264 codec in Velvet Revolver, but if that doesn't deliever a good rate, try lowering the resolution.
On 2. You'll have to chance the preview range in Menu > View > Range