Barh, typically all you need to do is fold down your rear MBUS vice removing it. In fact, it a good idea to leave it on and aligned in case you have issues with your scope. Most mounts are high enough to clear a folded MBUS.
Most fixed magnification prism scopes typically have good eye relief, many up to three inches so not generally a problem.
You certainly can use a 1x4 scope but again check your eye relief once you've established your correct length of pull.
There's an old saying that you get what you pay for and IMO this really applies to scopes. If you can't find a "good & affordable" scope now I'd wait and save your money for something better. Fixed sights, once aligned are excellent. However, as an interim solution you might find an optical red dot excellent. Plus when you do get a scope you can mount the red dot either above or at an angle so you have both capabilities.
With an optical red dot you also have an option to add a fixed power magnifier.
Lots of good choices. It would be helpful for us trying to answer your questions to understand exactly how you invision using the weapon. Is it mainly for CQB or what?
Regards