CJ,
1 You don't(at least we don't) request a loadsheet by ACARS. It is sent by the ops center automatically when it is ready.
2. ACARS is the general system that the aircraft uses to comunicate by datalink. The datalink communication is data that is sent on the back of a radio signal. These are VHF, satellite(UHF) or HF. Within the ACARS system we have 2 kinds of applications, namely ATSU and AOC. They operate off different ARINC standard and hence the difference. ATSU is how we communicate with ATC which is what we know as CPDLC. It also includes DCL(datalink clearance) which is how we get departure clearance from ATC.
The other application(AOC) is the one we use to communicate with the company. It has less stringent certification standard(than ATSU) and that is why it uses a different ARINC standard. Some of the uses include getting weather, atis, free text messages to maintenance, dispatch, etc. It also includes PDC which is pre departure clearance which on the surface is the same as DCL but it is different. With PDC the messages are routed through the company and DCL is direct with ATC. This is transparent to the pilot except for the fact that that a PDC is required by ATC to be read back verbally whereas DCL is accepted on the ACARS with no readback.
From this you can see that a plane can be equiped with ACARS but might not necessarily be CPDLC equiped, in which case it should have no ATSU menu.
3. You can configure anything to print automatically. Press the DATA key followed by LSK 6R(ACARS PRINT FUNCTION) and there you will see a bunch of things you can configure to print automatically(press the right arrow to see more options). Loadsheets always print automatically. I don't know why but it also does not appear in our messages received list(like your sms inbox) so if the printer gets stuck, the only way to re-print is to call ops and ask for another copy to be sent via ACARS.
We are moving to a system where we will print a loadsheet only for info. The actual loadsheet will be accepted by pressing a button on the ACARS.