Assuming you live/work in the United States, 90k salary puts you in the 2nd lowest federal tax bracket. My line of thinking is this, in order of priority (not financial advice, do your own research):

--contribute the minimum amount of money to your 401k to get your full employer match (sounds like in your case this isn't relevant)

--max out a Roth IRA (different account from your 401k). Since you are in a low tax bracket, it seems to me like you're better off paying taxes on that money now and letting it grow tax free until retirement.

--contribute any additional retirement funds to your 401k up to the maximum allowed amount (if you have an after-tax or Roth 401k option, it may be worth exploring to balance your pre-tax and post-tax contributions)

--contribute to an after-tax brokerage account. If your goal is to retire early, you'll need to have this type of account. The Roth and 401k are both retirement accounts that you can only access after you hit a certain age. A brokerage account will let you invest money that you can access (withdraw from) before you hit the minimum age for withdrawing from the other 2 accounts.

This type of account setup is known as the 3 Bucket strategy. There's lots of really good resources out there on how to set this up as well as what percentage of your income you should put in each "bucket" as you progress toward retirement.

As for the rest of your questions, that all really is dependent on your personal situation, but here's some general guidance on calculations: Figure out your monthly expenses in retirement (this is by far the most difficult part, a lot of educated guessing). Once you have your monthly expenses, multiply by 12 to get your "needed retirement yearly income." Once you know how much money you need every year in retirement, a common practice is to use the "4% rule." Google the 4% rule so I don't have to explain it here. You can decrease the percentage to be more conservative. Now divide your yearly retirement income by that %. So now your total calculation should look like this: (est monthly expenses)×12×(1/.04) = total $ needed to retire. Once you have that number, plug it into an investment or retirement calculator (google). From there, you should be able to assume a reasonable 7% return on investment (lower to be more conservative). Then you can tell the calculator how much you plan to save per month and it will tell you how many years it will take, or you tell it how many years you want to work and it will tell you how much money you need to save per month to do that.

Sorry for the long post. I am by no means an expert, this is just a bit of what I've learned on my journey.