Yes, "equipage" is a word. It is not a gygaxism.
The scope need not be restricted to the medieval ... This seemed a promise for various published settings for D&D that might stretch from the prehistoric to the imagined future. They did materialize, after a fashion, though TSR decided to go a different route. Rather than expansions or campaign-style releases à la Greyhawk, new games with their own unique mechanics were introduced (e.g. Boot Hill, Metamorphosis Alpha, Warriors of Mars).
Number of Players:
Much has been made of the from four to fifty players statement. Basically, campaigns could support a great many players but one should not assume there were fifty players to a single session. On any given night the number of players present would be similar to any modern day gaming meeting.
Also note: referee and other underlines for emphasis. When typing on a typewriter, machines in those days capable of italics were uncommon, so underlining was the standard alternative. Looking through the pages of these rules, one may perhaps wonder at the emphasis EGG chose to place.
Dungeons & Dragons (you have it!) Why, we must ask ourselves, did Gygax feel compelled to point this out? Whimsy? Completeness? Stream-of-consciousness typing?
Dice: note the lack of usage of dice notation (d4, d6, d8, etc.); this terminology did not appear anywhere in OD&D or its supplements. Instead four-sided, eight-sided and the like were used, with dice being understood to be six-sided dice.
Preparation for the Campaign:
In spite of promises the rules will cover how to set up and actually play the campaign? This is one fo the few direct examples of actual advice on how to do it. D&D spread largely by gamers playing with an established group who then went out, bought their own rules, and began their own campaigns (though there were exceptions, including your esteemed editor).
This gave rise to a free-wheeling anything goes kind of campaign. Players had no guarantees about what they would see, their player-characters could do, or the exact nature of the setting until they sat down and played at a referee's table. There was no correct or incorrect way to play, and this aspect of gaming is one missed the most by players around during that time.