You don't need to know the exact tooth count. If 3 significant digits isn't enough precision for you then your head will explode once you factor in tire expansion at higher speeds.
Good overall summary, but one small note. Gear ratios are not approximations. Gear ratio is the ratio of one gear to another. It is an exact number. If you have 40 tooth gear to 10 tooth gear it is 4:1 ratio. There are no variances or manufacturing tolerances on the number of teeth each gear has.
Overdrive just means that the ratio is less than 1. Nothing more, nothing less. There is nothing magical about this.
4th is 1.02. Just change it by 0.03 and it magically becomes yet another overdrive gear.
4th = 1.02
5th = 0.89
6th = 0.69
So if you want only 1 overdrive gear, what do you...
Virtually all Hondas use the same filter and washer. S2000 may be the only exception. For our cars you can use washer designed for any of the Civics, CR-Vs, Accords. I bought these several years ago and use them on all my cars (2018 Civic, 2010 CR-V, 2008 Civic, 2007 Accord)...