I'm planning on doing a one-shot to test out some new friends, and was hoping for some advice.

This will be my first time DMing AND playing D&D, bear in mind.

Given that I'm not certain that this will be a long-term thing, I figured that a one-shot would be ideal, and that I could extend the story if my players feel invested. I wanted to try homebrew in order to be more connected with the environment we're envisioning. Having watched a decent amount of D&D streams (Critical Role, one episode of Urealms, though I wasn't a fan of that) i feel pretty comfortable with how a game might progress -- I've also read a few DM tips on this subreddit. What I'm not certain about, however, is where to START. I mainly worry about having interesting challenges for players, fumbling with rules (I haven't bought the books as of yet since they're expensive and I don't know if we'll keep playing), having an interesting main conflict, and actually having fun myself even though I'm not playing. All I have as of right now is a couple flavorful NPC's, but I plan on diving into it within the week. Any advice, especially about starting out with a homebrew, would be great. Thanks!