Since diversification is so effective at lowering risk, should I focus on building a balanced portfolio first and then use research to fine-tune it, rather than just picking individual stocks?

I have one question regarding this as well:

If RSUs were granted while I was working overseas but vest after returning to the U.S., how does the IRS determine which portion is subject to FICA? Is the entire vesting value taxed, or only the part tied to my U.S. service period?

The interest rate of floating-rate notes is adjustable periodically, so my question is how they adjust their interest rates, and how do changes in interest rates affect the value of floating-rate notes?

I work for a small-scale company, which does not provide health insurance for employees. But I need to apply for any health insurance. Is there any health insurance available that offers a comprehensive check-up and is also affordable?