Before we start, I'd like to note this is not for Walkthrough questions, or "how many elements do I need for a spell" type things. This is more for how the game works. I can't answer everything, though.
Q: How many playable characters are available in this game?
A: Sadly, only 1 on every version available. However, there was a plan for two more party members. They have been confirmed from Beta Screenshots as Kiliac and Princess Flora Scottford.
Q: How many versions of this game exist?
A: There are 3 actual versions. And one full remake. For the Nintendo 64, you can play Quest 64, a direct port in Holy Magic Century(in various languages, to note). And finally, there is Eletale Monsters, which is technically the same game, but has a bit more story and many additions to the original game.
Q: Does this game require a Memory Pak to save?
A: Unfortunately, it does. You can store up to 16 saves per page.
Q: Why are there no shops in this game?
A: While this was indeed planned, the creators were completely rushed, omitting some things like a monetary(money) system. However, the game's design makes the need for a shop unnecessary. While you can't easily stock up on items(except the Japanese and Gameboy Remake), you can still rather easily beat this game through training, or grabbing Treasure Chests.
Q: I heard you could ride a Horse.
A: Yet another thing that didn't come to fruition. It's not necessarily a bad thing, though, as walking around actually increases your Agility anyway.
Q: Why can't I read the signs?
A: Besides the obvious answer, this actually does get implemented in the Japanese and Gameboy Remake versions.
Q: How many NPC's are in this game?
A: ...Let me get back to you on that. However, there's well over 200 unique ones. All with unique dialogue and names.
Q: How many bosses are in this game?
A: Exactly 8. The Gameboy remake adds quite a bit more.(four major ones. And some monsters appear early, but aren't ridiculously tough.)
Q: I heard there was a sequel?
A: Only some of it was leaked. It never came even close to being made. One theory is that it turned into Aidyn Chronicles: The First Mage.
Q: What's the point of the Night and Day System?
A: Nothing, actually. It has no effect on anything whatsoever. However, it was meant to affect enemies, specifically, who appears. However, you can actually save and see how long your character has been around for.(months, days, etc.) Every time you "rest" at an Inn, you add one more Day/Night(as in 12 hours).
Q: I've noticed the name Epona in this game. Isn't she the Horse from Ocarina of Time?
A: Not exactly. This isn't the first game to use the name Epona, but many have well before Ocarina of Time. This game uses it for a female human character who appears to be able to Travel practically anywhere. She may have created the Wings that you can use for Travel as well. In addition, both characters in question are named after the Horse Goddess of Travel. Very fitting.
Q: How many Monsters are in this game?
A: Exactly 76. With the regular n64 Bosses, 84. In the Gameboy Remake, 76. With bosses, 92. You sometimes re-fight certain bosses with different stats. That's included, however, boss fights against regular enemies(since no stat changes occur) are not listed in this total.
Q: How can you leave Mammon's World?
A: You must let yourself get killed and you must have saved somewhere outside of Mammon's World itself so you'll get sent back to that spot. Using Return or Exit will not bring you out of that area. This is actually programmed into the game that way.
Q: Do your Elements have any effect on Experience?
A: It is unknown. In fact, nobody has ever successfully been able to determine if things like more Fire let you get more MP experience. It has never been truly tested, and while some FAQ's give information, it's based solely on an emulated copy and may not reflect the actual official games. For those who have read Fire_Embliem's Combat FAQ, keep in mind he used an emulated copy for all the data collected. This does matter and it means his data, while good, is not guaranteed to reflect the actual N64 game. Use it at your own risk. However, I do believe his data seems completely accurate. It would be neat if Elements did, but there has not been anything more than rumors/speculation on that.
Updated a little with more information. Also, any questions are welcome(via PM or a reply here) and will be added in.