The microscope and delta stage will both operate as high resolution microscopes. The main difference is in the configuration of the motion. In the Microscope version the motion has independent actuators for the three axes x-y-z. The stage is moved in x-y by two actuators and the optics module is moved in z by the third actuator. In the Delta Stage version the optics module is fixed and the stage moves in x-y-z, but there are not separtate actuattors for teh three axes. To move in z all three actuators must move together. To move in x or y two actuators move together and the third in the opposite direction. With motor control this calculation is built into the software if you select ‘delta stage’ in the settings, so you can just ask for motion in x, y or z as required. If you are moving by hand the Microscope gives the intuitive motion. The Delta Stage is in principle better for heavy optics as the optics are fixed rather than hanging on a moving actuator. Otherwise the optical performance is the same. The Microscope has the stackable bucket bases, so if you are wanting extra or non-standard electronics that gives a good way of housing them.
The fasteners and illumination kit is the parts needed for the Microscope version. The Delta Stage operated as a microscope requires most of the same parts. The optics modules, illumination and actuators are basically the same. The difference if any will be in the number and length of M3 cap head screws required.
I don’t know what is different about the 8GB Pi that caused problems, or whether that is still the case with the current version of the server.
The Pi High Quality Camera has a different sensor size and would require a different optical system. use the PiCamera V2. See this thread Support for HQ Pi camera - General - OpenFlexure Forum