[GNC] importing simple investment account

[ar]

Hi,

I am downloading my data in the form of .csv file and I have a simple
program to generate an.qif file with proper categories and then import .qif
into gnucash.

I am adding a program to deal with investment accounts. The problem is that
GnuCash investment account consists of a multitude of sub-accounts: cash
sub-account + one sub-account for every security/mutual fund.  Should I
generate a separate .qif file for every sub-account or I can pack it all
into a single .qif file with proper account headers inserted?

Also, I would generate .csv files but it is not clear what is the native
import format for bank and investment transactions.

Also, I am using 3.x GnuCash, does it make sense to switch to 4.x to
simplify my importing chores?

Thank you,

Aleksey