All game-development starts somewhere, but does it functionally matter where?

Let's imagine all the concept art and over-arching planning is done. Unreal Engine is being used. I know basically what product I want to create (obviously that will change as iterations prove to be more or less fun/rewarding/possible).

I've opened up Unreal Engine once again… and I'm thinking: Where do developers start to ensure in a years time I don't go to program something and realise: “Oh, dear… That mistake I made on day 1 has crippled the project.” I intend on the game to have a range of maps/biomes in the future. I had thought I could start by making 1 map/level/playable-area and referencing it as… let's say DrylandsBiome01.

If I program hundreds of mechanics and features while working on that map;

• Does that hurt me when I go to make another playable area like WetlandsBiome02 or SnowlandsBiome54?
• Will I be able to just “sub in” a new map and retain my core game mechanics and features?

TLDR; if I build a map and then start adding actors, assets, features and mechanics does that hurt me when I go to make another map? If so, where should I start then?

Apologies, the site glitched as I was posting and deleted my whole post. I will re-write shortly.

My occupation is a Business/Systems Analyst so my “start” is before a line of code is written. I'd suggest writing down your idea; just a paragraph or two. Then, start picking out your nouns and verbs from that text. Your nouns will generally become your classes/structures and your verbs will generally become your methods/functions. Then sketch out the rules you want to implement.

After that, you'll want to considered how to approach the coding. Break up your work into small tasks. User Stories are a good approach to this as it states the goal and the criteria you need to determine if you've reached your goal.

I'm conveniently ignoring a lot of detail here but this is a high-level description of how I think you could get started.