Hi, vga4Him--Glad you're enjoying looking at your Geneva Bible. Looks like JBI and Whifflingpin have already answered some of your questions. I study and teach literature from the Middle Ages through the Renaissance, and so am very familiar with the language from that time. You are right that the Geneva Bible is Early Modern English, from roughly the same period as Shakespeare. It is much different from Middle English, the language of Chaucer, and even more different from Old English, the language of Beowulf.
In terms of the s/f usage, Whifflingpin has already given a good account of the short versus long s, also known as the miniscule and uncial s respectively. As he pointed out, the character for the long s looks like an f, but doesn't actually have a stroke all the way through the letter. This is a pretty clear image where you can see the difference:
The use of the long s derives from the look of the s in late Roman script. Here's an example from about the 4th century, though variations that looked like this occur throughout the middle ages:
The mixed use of short and long s developed in the manuscript tradition of the Middle Ages, much like many of the characteristics of early printing.
Yes, you're right that the abbreviation mark usually indicates a letter m or n to follow a vowel. A common mark is the little wavy line, called a tilde (~) over the vowel. The use of this abbreviation was, again, a practice that developed in Medieval manuscripts. It was partly just a way to make writing faster, the way we currently use apostrophes for abbreviation. In addition to convenience, one reason for using abbreviations in both manuscripts and early print was that the ink and paper required were expensive so space saving measures were important (there are even more complex abbreviations in medieval manuscripts to get as much use as possible out of each page). You may also notice that some words are written partly in superscript to save space, especially with common abbreviations like "wt" witha superscript "t" for the word "with."
Actually, words like judgement were usually pronounced with a "J" sound, though they were spelled with an "i". The same letter was used for two sounds the way that in modern English the letter "c" can be both soft (cipher, city) or hard (caper, cat). The letters "y" and "i" are also often used interchangeably, and "v" and "u" were also often typed as "v" in this period, and you'll sometimes come across two "v"'s tped one after another, or a double u. Hence our modern "w." Another confusing usage you may come across is the use of "ye" for "the." "Ye" was actually still pronounced the way the modern "the" is, but was using the "y" as a replacement for the thorn, originally an Old English character for the "th" sound that persisted through the Middle Ages and looked much like a "y" in late Medieval manuscripts. An example of a 12th century manuscript thorn:
As both JBI and Whiffling have pointed out, spelling and grammer in this period was not strictly regulated, and spelling in particular was just not considered an important convention in the way it is now. It wasn't until the 18th century that you see real attempts to come up with standardized spelling and the like. Similarly, there weren't strict conventions in terms of capitalization. The use of capital letters is fairly idiosyncratic in the period. Some texts use capitalization more consistently than others. In some texts capitalization appears to have been applied quite randomly where the author wished to create emphasis. My memory of the text of the Geneva bible was that it utilized capitalization to apply emphasis to possibly significant words in the scripture.
I think that covers most of your questions. Feel free to post any others you may have about Early Modern texts or related concerns.