@Nico that looks cool. For your questions about scanning, tiling and resolution @JohemianKnapsody has been doing some work on tiling, measuring resolution and getting good z-focus and recording focus stacked scans. There is a thread on the tiling images Automated Slide Scanning and Tiling.
Oil immersion objectives seem to be usual for blood samples, whether the microscope is upright or inverted, it is not something that I have looked at myself. Post 6 from @david on this thread High-resolution, upside-down microscope for oil immersion has practical suggestions on oil immersion with inverted microscopes.