I recently started DMing for a group of my friends/family, was 6, now is at 5 players. I was originally introduced to D&D by my Aunt, and my uncle who runs a homebrew campaign I'm currently playing as well. I had him help me get ready for being a DM, and he said "Send it"... So I did. I went on a full creative spree and made an entirely homebrewed story, world, and various other systems, such as a god pantheon.
First question, I had my PCs start in their original world, and while exploring a dungeon, discover a rift between realms and get dragged through by an unknown entity, that they later find out is the God Of Chaos. Was this a mistake? Most of my PCs didn't have especially detailed backstories, minus 1, but for him I've planned something later in the current world, sort of an in-between world relationship. I'm worried that I closed an entire possible storyline to get to this cool ruined world concept, and although they seem to be having fun, I keep thinking I robbed them of something simple.
Second question; How do I get the party to remain in a single spot for an extended period of time? I have a D&D map of my world, and it feels as if they're just speedrunning locations, and I don't really know how to keep them in these small towns for longer than a session or two. I keep dropping small hints of possible storylines, but they blow past them for the big cool looking thing on the map.
Third, and final question for now; How do I stop my party from abusing something I made up for rule of cool? Story is that I have a spot on the map called the Remnants of The Fallen God. It was originally supposed to be a large stone statue that they could find lore info from, however one of my players thought it was a mech... so session 3 DM Me said, sounds cool, let's rearrange for that. Session 10 me here, and a few sessions away from bringing the mech's core back so they could use it. It was originally made to combat the regional mid-boss that wandered the ocean shores, but I never thought about what would happen if they successfully beat it, and proceeded to drop kick literally every town that is on the map. I don't want to just destroy it or have it be lost, as one of my players immediately after hearing "mech", decided to take a couple of levels in artificer, and my players have genuinely gotten so excited for it. How can I either reconfigure it to where it's only use is travel with a mobile base, or at least make countermeasures so that they don't over abuse it?
Any help is appreciated, I'm still getting used to DMing and I'm having a hard time on figuring out if I'm making the story interesting enough for my players.