The definition of casually for this post: Doing other things besides focusing on making money.

I made over 250k( that's what i had in cash after expenses) in my first 30 days while still obtaining level 50, leveling crafting professions, doing battlegrounds, dolemens, and quests, dungeons, fishing, and socializing.This was playing 3-4 hours a day every day. If you focus on making money, i see no reason why you cannot hit 750k in your first month playing 3-4 hours a day. Here is how i did over 250k while still partaking in everything the game has to offer(at low levels):

1) First you need ESO Plus for the crafting bag/double bank space. Not having it will hinder you (greatly).
2)Addons: You need HarvestMap, Awesomeguildstore, and Tameriel Trade Centre(TTC) addon and website
3) A sneaky toon is best. For example i used a wood elf nightblade.
4) By level 20 at the latest you want to be in a trading guild. You want enough stuff to warrant being in one. Most cost 5k to 10k a week but i got in a good one that was free( i sell 20-30 items every 24 hours in it and restock only once a day)
5) You will want to expand your inventory and bank space as needed I had 100 inventory and 160 bank space after a month.

So here is what you do after you have ESO Plus, addons, and a character made:

1) Play the game normally. Quest, explore, whatever. Loot/harvest everything. Newbie zones tend to have plentiful amounts of things to loot/ gather available making them a great place to farm.
2) Learn the lockpick minigame for chests and locked doors. Chests sometimes have worthwhile loot, but usually just blue or green gear. But picking the lock helps level ledgermain, which is important.
3) I deconstruct all gear that is not ornate that i am not using. I only kept and banked purple gear for future toons.
4) You want the skills that highlight resource nodes under the crafting skills. One point is enough in each. It will make finding resources much easier.
NOTE: Loot dungeons as well. I loot all mobs. You can loot containers as well but i recommend only snagging one or two as you run by them, so you dont annoy group members. I also loot after the dungeon is complete.

Phase Two: The money making part.

So now you got you a good stock of stuff, your in a trade guild and you made it out of the newbie zone. Now what?Time to hit the banker.

Note: I added all recipes, blueprints, motifs, etc to my collection first and sold doubles.

1) When you are ready to start selling load your inventory full of things you want to sell at the banker.
2) Open TTC website( i do this on my phone) and use the price check feature.
3)Check the price of your items and list them in the store. I usually go near the bottom of suggested list price. Fill the store with 30 items. Recipes, motifs, and crafting material sell the fastest.
4) Now its time to get your thieving on. You want to find a place with few to no guards. Buildings that are upper class such as noble houses, manors, castles, etc tend to drop better loot on average. While areas that are more poor such as docks, slums, etc tend to mostly drop ingredients and white gear.
5) While sneaking you want to steal valuables from containers. You are looking for valuables of the type "Treasure". These have set values: 40 for white, 100 for green, etc. You also want to steal recipes, patterns, motifs, etc. Anything you can launder for a profit later.
6) Once your inventory is full its time to head to the outlaw refuge and fence. Fence all your treasures, then swap to launder. Learn any patterns, recipes, motifs, etc first if you are going to learn these things. They don't need to be laundered to learn, just to sell. Launder everything that needs laundered and bank it to add to your store later.
7) Repeat this until you have maxed out what you can sell to the fence for the day. Make sure you max out both sell and launder everyday. I use provisioning ingredients to finish off my launder for the day. they are cheap and it takes very little time to steal 1xx ingredients. Its important you max this out everyday to level ledgermain. Higher ledgermain means better items spawn in containers which means more money.

Phase Three: Perfecting Your Profession

1) You will want to put skill points in relevant skills related to ledgermain, thieves guild, dark brotherhood, and any other skill that helps you steal everything not nailed down without getting caught.
2) Use harvest map( You have been gathering resources haven't you?) to find the highest concentration of nodes of a type( or highest concentration of nodes in general) to maximize your farming.
3) Remember good spots for certain things( I write mine down). For example i have recipe/treasure spot i farm like no tomorrow when i don't feel like randomly stealing or exploring new spots. I have a place where i gather flour, cheese, meat, game, honey, etc. I have places where i gather certain alchemical ingredients. So when i'm looking to restock/sell something i can quickly obtain it.
4) Do the thieves guild and dark brotherhood quest lines early on. They will enhance your money making ability. They are accessible with ESO plus. NOTE: Mobs level with you. So you can go (almost)anywhere in this game from level 1 as long as you can physically get there.
5) Learn how to steal from places like banks, locked houses, and vendors( safeboxes).
6) Learn how to pickpocket and assassinate npcs. (Dont forget to level the skill "swiftly forgotten")
7) Learn what sells and what doesn't. Its often better to move a bunch of lower price easier to obtain items, than it is to move one large ticket item and have to wait days for it to sell.
8) When you can farm enough stuff to sufficiently keep one store stocked, you may want to consider a second trade guild( You can be in up to 5 player guilds at a time)
9) By the end of your first month, your ledgermain should be around level 20 and you should be selling around 20k worth of treasure a day to the fence plus doing another 2-5k/day in the store.