It should be possible to schedule stock or currency purchases. Currently, I
have found no way to set the exchange rate or share price in scheduled
transaction.

[Practical use: I have a voluntary retirement pension scheme that lets me
accumulate "points". The money is withdrawn from my salary. I know in
advance how much money is withdrawn and how many "points" I buy. I also
know my salary and the approximate date it is paid. So it is sensible to
set up a scheduled transaction like this:

debit salary from employer income account
credit checking account
credit pension scheme by x points]