Depends on how much they have, where their retirement comes from, what a steep drop in this investment would do to their retirement, and how much risk your parents can tolerate.

Rent money does not go "down the drain." What house are you going to buy with less than $10k down payment?

The January 2023 estimated tax payment is for the 4th quarter of 2022.

First, you're not a "W9 employee." W9 is just a request for your tax ID and does not imply any kind of employment. You're self-employed and you may receive Forms 1099-NEC from your clients / customers. That is income you will report on Schedule C of your Form 1040 tax return. Schedule C is also where you will deduct legitimate business expenses.

Most likely you will run your business on a cash basis just like your personal taxes are, which means you record the income when you receive it, not when you send the invoice. In your example money received in January is taxed next year.

Estimated taxes are paid in April, June, September, and January. For your first year of self-employment, take the "total tax" from last year's tax return, divide by 4, and make that your estimated payment. Open an account with EFTPS.gov for making Federal payments and look into your state's online systems for making state payments.

You may want to open a separate checking account to keep your books separate, but you should not need multiple accounts. You should learn how to keep basic business books though.

One thing you might not be aware of is the self-employment tax. You now have to pay both the employer and employee halves of Social Security and Medicare tax.

I'm not sure you can file W2 before January 1. Try tax1099.com in a week. It will cost you a few bucks to e-file but it's worth it.

Are you not able to deduct your traditional IRA contributions on your 1040?

If you plan to hold the stocks long term in a taxable account, you should prefer to buy on/after the ex-dividend date.

Get a brokerage account and save there. REITs throw off a lot of taxable income. Better to hold a REIT index in the IRA and hold stock index funds in the brokerage account. If you own the stock market or the S&P 500 you already own a bit of the most productive and profitable real estate on Earth, making REITs somewhat redundant. Don't put too much of your savings in REITs unless you need the current income.

My asset allocation already takes the bad years into account, and rebalancing helps me make the most of them.

The target date fund is really a bundle 4 or 5 different diversified funds. You can be comfortable making it your only fund. Vanguard Target date funds are good and the expense ratio should be low, but you should check. If you want to be more aggressive you can choose a later retirement date than you ordinarily would.

Despite the downward trajectory of bonds over the last year, in general the bonds will not be as volatile as stocks. At age 17 the moderate portfolio is all in bonds and short-term reserves, and the aggressive portfolio is 25% stocks. If you've split 50/50 you're only 13% in stocks and even if they got cut in half you'd only be down 6-7% and your bond funds would almost surely go up. I think the risk of a 30% haircut between now and college graduation is extremely low.

Even if you had a gain it doesn't create taxable events in a Roth IRA.

I'm not sure you should change anything. The age-based portfolios will continue to move you into bonds, and while bond prices may continue to fall short-term, bond yields are up. In a way you should be glad bond prices have fallen while you continue to buy them. If your risk tolerance had you allocated somewhere between aggressive and moderate all this time, why change now? Are you now unwilling to risk any decline in the balance in the next 2-6 years?

Changing the present value of the loan from $100k to $75k calculates a completely different payment, so you can't CUMIPMT in that way. Paying extra on a loan reduces the number of payments, so you could use NPER to calculate the number of periods with a given payment, then calculate CUMIPMT of the original loan between that period and 360 months. That amount is your savings.

However, I question the reasoning behind your goal. Calculating cumulative interest over 30 years ignores the time value of money and gives a misleadingly large amount. The present value of the interest payments should be how you compare the two scenarios.

At a T-bill auction most investors enter a non-competitive bid. You are bidding for the amount of T-bills you want and agree to accept the auction price, whatever it turns out to be. Large investors and institutions enter competitive bids, indicating the rate/yield that they will accept. Those competitive bids help determine the outcome of the auction and the rate/yield you receive.

I wouldn't recommend trying to pick your own stocks. You should buy a total market index fund or ETF. The next Amazon probably won't be Amazon, and you'll have a better chance of owning some of it if you own the entire market.

I-bonds with a high fixed rate were available years ago. Those would be good to have now and in the future. Today's I-bonds have a very low fixed rate. If and when inflation goes back to normal you'll have a fairly low-yielding bond with a very small premium over inflation. Any guaranteed return over inflation is desirable, but I think you need to put some of your capital at risk to earn better returns if you want to fund a retirement. That means stock markets, other parts of the bond market, etc. I think for people who have not or don't want to put the time in to learn all this stuff, the best way to save for retirement is in a tax-advantanged account like an IRA, RothIRA, 401k, etc., using a retirement target-date index fund. Those funds take appropriate risk for your age and reduce risk as you get closer to retirement. Start there.

KO dividend yield is 2.96%. You can get 4.4% from a 1 year CD. Still want to buy Coke?

Don't make your investment decisions based on what is promising the highest return. There is no such thing as high yield or high return without high risk.

Most stocks that pay a high dividend have a very high chance of having that dividend cut. It's a pretty good way to lose money.

In the 12% bracket the Roth is a great choice. It's costing you 12% in tax to make those contributions, but after tax free growth and withdrawals you will almost certainly come out ahead. When you get to the 22% or 24% bracket and above, the benefit is less clear, at least to me. I think in 24% bracket it can be better to make Traditional contributions plus invest an extra 24% taxable. Even though you'll pay tax on withdrawals, you'll end up with around 24% more savings, and that can pay for a lot of taxes in retirement.