What to do after you maxed out all tax advantaged opportunities?

After I maxed out all tax advantaged options, there is nothing else left for me then to open a taxable investments account.

What taxes would I pay on investments in a taxable account?

A taxable account is funded with post-tax money.
The interest, dividends and capital gains are taxed every year. 

1. Interest
It is taxed at ordinary income tax rate according to you tax bracket.


2. Capital gains and Qualified Dividends (2018)
Ordinary dividends and short term capital gains are taxed at ordinary income tax rate.

Qualified dividends  and long term capital gains are taxed at reduced rates: 

There is an additional 3.8% Net Investment Income Tax (or Medical Surcharge Tax) for capital gains, and dividends.
It applies to modified adjusted gross incomes exceeding $200,000 for singles and $250,000 married filing jointly.  



I am thinking of opening a separate "challenge" account in which I will try to learn how with certainty to achieve more than 1% yearly returns on my own. In this account I will not use indexing. 
Majority of my investments is in index funds at this time. Indexing is supposed to make more than 1% returns per year with relatively high certainty. 
The "challenge" account will be for trying it on my own. I will add a link to it here as soon as I start with that.