Best way to understand upgrades/synergies?

Playing DE after playing Age of kings... ages ago. Really impressed with all the new civs, the community, the wiki, and all the campaigns.

Sometimes I'm a bit confused about how certain upgrades apply - for example bulgarian increase to cavalry attack, which i assume does not apply to cavalry archers? Similar issues with "archer" upgrades and whether they apply to skirmishers and cavalry archers (edit: and do they all apply to hand cannonners?) .

Hovering over tool-tips helps in some cases, but there seems to still be a lot of ambiguity with how units are classified? also the hidden bonus damages i've learned about seem to be pretty significant. Is there a basic flow chart/info-graphic to help me understand all of that?