Having the engine before building the fuselage makes it easier to set up the firewall for engine mounting but is not absolutely necessary. And, if you use an adjustable mount (such as Great Planes brand) you do not need the engine yet because the mount has a template for drilling the firewall.

You could use as small as a .70 size four stroke on the plane but an .91 to 1.00 is most commonly used.

I had a .70 on an Astro Hog (similar size and weight) and it flew very well. Nowhere near unlimited but very capable of loops and basic aerobatics.

You can use CA or wood glue for everything that doesn't specifically call for epoxy in the instructions.