Levels of derailleurs, freewheels and chains
The higher end groupsets (Alivio and above) would not be the right Speed as you plan a 7 speed freewheel and they are all 9 / 10/ 11 speed.

Shimano's webpage has in the Trekking section:
Acera - 9 speed,
Alivio - 9 speed,
Deore - 10 speed,
Deore XT - 10 speed

In the Mountain bike range there is (lowest first):
Tourney TZ,
Tourney,
Tourney TX,
Altus,
Acera Altus,
Acera,
Alivio,
Deore,
Zee,
SLX,
Deore XT,
Saint,
XTR

I think the only derailleurs Shimano would say that work with 7 speed would be the Tourney rear derailleurs and the Acera RD-M360 8 speed derailleur, unless I've missed some.

But I can't see a reason that a 9 speed rear derailleur wouldn't work as the actuation is the same. The cage may possibly be fractionally narrower as its designed for the narrower 9 speed chain but I have heard of people running this with no issues. You would have to use a 7/8 speed chain though and not a 9 speed one.