Forgive me if this is a noob question but when you say taxable investment account do you mean Roth IRA?
Not sure if its better for me to use the money I could put in roth IRA into 401K instead. Or is it good to have both?
Taxable investment account is one that's free and clear of IRA or any other rules, but investments held in it are taxable(the gains made). By contrast, a 401k is taxed when it's withdrawn as income, and funds inside of a ROTH IRA are never taxed because they're post-tax money you have(and that's why the contribution limit is so low).
Myself, I jumped in with taxable investments before really considering the tax side of things. I've since switched to maxing my ROTH contributions and 401k, but it's really nice to know you have a lot of money outside of the tax shelters, that you can do anything with at any time. I don't keep much of an emergency fund... about 1-2 months because I have a lot of money in my taxable investment account which I consider my true emergency-emergency fund.
There's benefits to both the ROTH and the 401k, and IMO you should have both. The 401k itself, depending on your employer, you may be able to contribute after-tax earnings to it, which then fall under some of the ROTH rules. The benefits to the 401k is that your using pre-tax income to invest, and you may retire and draw it down in a no-income tax or lower-income tax state. The ROTH contributions on the other hand can be withdrawn at any time, but you only have(currently) 5500$ to deposit in them per year. Slipping in pre-tax income into your 401k, combined with the employer match will really raise your net worth a lot quicker then anything else, so it can be pretty motivating to see it happen.
So, there's
-ROTH IRA
-Traditional IRA(if your employer has a 401k plan, not really worth looking into that much, except for the roth pipeline if you ever FIRE before 60)
-401k
-Roth 401k
-HSA
As for your fund choices
-Stable value fund is a cash holding option that should be ignored for all ages before 80.
-I'd put a little bit at least of your money(>10%) into the non-US and the emerging market index funds. You can read the prospectus and find out some of the biggest holdings to understand who it's investing in. The expense ratio cost for taking the "Portfolio" vs index fund option is really high so it's not really worth looking at that much.
You're with Fidelity, so the target date funds likely carry ~.8% expense ratio's, and you can achieve your own "target date" fund with a lower expense ratio by diversifying across sectors, and by using the (100-age) rule of thumb for bonds