Hi all - this is my first time posting in this subforum, as I usually hang out over in the media area. I'm hoping to get a bit of advice, and maybe share a bit of what I have going on.
Spoiler: Background - me back in gaming
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Basic background on me - I was a regular player way, way back, and DMed a lot of games with the AD&D 1st and 2nd edition rule set. I still have a number of books from that time frame, like the Monster Manual that came in 3 ring binders, Fiend Folio, and such. The last book I got from then was Creative Campaigning - I know this, because it was on top of the stack when I recently got out my old books.
Cut to now, when I decided to join a game as a player. I got the new Player's Handbook, read it, and joined the game. Well, I was the odd person out - I only knew the DM, while everyone else had been friends for years. Turned out that there was one player who basically ran the game, because everyone just bowed to what he wanted. And what he wanted was to be a nominally good character who killed merchants because he didn't want to spend money, while at the same time bullying the DM into handing out more and more loot. I did not last long with that group, but between that, frequenting here, and reading Darths and Droids with the gaming tips, I decided to create a campaign. We had our first session yesterday, and while everyone said they had fun, and I'm positive two of the three players did, I want to try to make things better. Hence, request for advice.

Spoiler: Background - campaign quirks
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Basic background on campaign - I write short stories in my spare time, and they are all set in a specific world which I have adapted to the campaign. The central conceit that makes it different from most is a third axis of alignment, and a set of deities that flow from that. The third axis is nature/civilization. Imagine if you will a 24 sided figure - think a six sided die where each side has a little 4 sided pyramid, adding to 24 sides. The tops of each pyramid is one of the extremes, and the opposite side is the opposing extreme. The eight total corner points of the original cube represent where the three major factors come together - where law, civilization, and good combine, you have justice, while law, civ, and evil are pride. The four sides of each pyramid represent the deity that fits the three corners of its triangle, so there would be four deities of law, with one of the four specifically being where law and civilization meet on edge, representing law, pride, and justice (he's the deity of attorneys and bureaucrats).
The other major thing that sets it apart is that there is an old world, which is fairly close to a standard high fantasy setting, and a new world that has been using less magic as technology has advanced. The new world knows about the old world, but the old world has been through enough upheaval that most do not know it's there and was once colonized by the old world. The new world is on the cusp of guns, although there are only a very few available.

Alright with that out of the way, I have some questions. I think I'm good at preparation. I had three different campaign themes ready, and we did a session zero where we discussed characters and theme. They unanimously went with high fantasy, good vs evil. Great. Two of the three (our fourth is currently on night shift, and is joining for session 3) wanted to start with 5th level characters, and the third didn't care. I compromised and went with level 3, so I wouldn't have to throw out as much material, and because level three is where the real campaign hooks begin. (I feel like I probably made a mistake allowing them to direct that, but it's too late now, and I'm OK with it.)
The first issue I'd like some advice on is dealing with different gaming types. It is clear at this point that I have one fairly shy player, one goofball, and one who is a combination of min/maxer and serious role player. To explain the last one, he's is the type to go to guides on the internet, youtube, whatever, to look for what is the most efficient methods for playing a character. During the actual game, he is very in to roleplaying the character he has, but the character is definitely the result of min/maxing. The first specific issue is between him, who is MM from here on out, and the shy player, who is Mal. Mal is playing a standard human ranger, and he picked skills and attributes that he liked and wanted to play. MM saw this, and tried convincing him that he should instead be a variant human so he could get a feat, and went on about how some of the choices for skills weren't ideal. Mal was fully prepared to change his character to fit what MM wanted. This was all during session zero, and I had to meet Mal separately to help him write up his character. I assured him that its his character, and he is free to make it in any manner he wants. He decided to keep to his original plan. At our first session, MM brought some stuff up again to change his character, but the goofball jumped in to defend Mal's choices, and we went on. Would I have been better off discussing as a group, or perhaps taking MM aside to talk about it, or was allowing the players to work it out themselves a good idea?
Now, for the goofball. Great guy, has the most current roleplaying experience, plays a paladin, and I expected him to be the most serious about playing. Instead, he's a goofball. Now, I've played with goofballs in the past - heck, I've been one. I played as part of a two wizard team, and we had synchronized somatic components that we'd act out together. I love goofballs, because they keep things fun. But I'm not sure how to handle the goofball if they come into conflict with someone else. While MM was looking through the eyes of his familiar, the goofball started to stack stones on her head. If everyone was a goofball, it would have been great. Nothing bad came out of it, as MM just laughed, but I could see possible problems. Any ideas on what to do if it comes to be a problem?
This is getting long, so I'll address my other major question, pacing, later on. If you have advice on handling player interaction, I'd love to hear it. The book I mentioned, Creative Campaigning, talks about it, but I didn't find it very useful for this.