Filed extension - what's my next best move?

Hi, I live in California, am mostly self-employed. I've been working on my 2018 taxes, and using both turbotax.com and tax.creditkarma.com to compare entries to see if one is better than the other. 

I work in tech, have 4 sources of income, and don't have a lot of expenses. After deductions, it looked like I would owe about $12k.

I filed my first ever Federal and State extension yesterday and haven't paid anything yet. I am concerned about penalties.

I have some small investments, I didn't even list them in either program:
~$100 in an IRA
$500 in fundrise.com
$100 in swell.com

Through turbotax, Live I think, I was able to speak with a CPA. She was really cool, and she showed me options if I invest in either a Roth, SEP, or Keogh IRA, I could save a little bit. I've learned that the Roth option expired 4/15, but the others I have until later to do so.

Seems it's a 10:1 ratio, that is, if I put in 10k, I can save 1k on my taxes. Not a huge draw.

I've been interested in buying a house, and was told it's advantageous to show more on my tax returns, although, honestly, I want to pay as little taxes as possible. I'm eyeing the installment plan.

Back to penalties, I don't want much, if any, and of course, have proper investments.

Since I haven't paid anything, and want to keep the amount owed down, and keep the penalties low or away, what's my next best move?