Can I go through tax return process roughly to get an estimated tax that I need to pay and file a tax extension for now?

[taxreturn1040-ta]

And by 10/15/2019, can I come back to the unfinished (typed most sections) tax return to e-file with additional information? I need more time to calculate numbers, but I do not want to pay any penalty by paying less tax by 4/15/2019. 

[fanfare]

you have to estimate conservatively.
In other words , pay a lot now.
It will be refunded when you file

[AlanT]

Yes, you can prepare your income tax return without going through the final step of filing.  You can file an extension and will have 6 months to come back and file.   All of your information will be saved in TurboTax.