Your Rottenfleiger is your wingman, his command list is first in the menu. (TAB + 1) You normally would do well to allow him to remain formed on your wing.
The first Schwarm (Schwarm 1) is your total flight formed by you as it's leader, then your Rottenfleiger (wingman) and the remainder of pilots. This is second on the menu (Tab + 2).
The second Schwarm would be any other aircraft directly under your command (TAB + 3 = Schwarm 2, TAB + 4 = Schwarm 3, TAB + 5 = Schwarm 4).
To give a command to the entire group (Staffel), you use TAB + 6.
A Schwarm can be a group of two, three or four aircraft, it all depends on the mission and/or flight strength.
If I wanted my flight (Schwarm) to tighten up on me during a mission for example, I would press TAB + 2, then select number 8, then select number 3. They'll acknowledge, and move in closer to my position.
The best thing to do, to get in some practice with your commands, is run some quick mission rounds, with all four Schwarms and without enemies present. Then as you get a little more familiar, add a few enemies and sick your Schwarms on them.
As far as the radiator goes on a Bf109, I've never noticed any reduction in speed if I leave it open, and in the "closed" position, it opens and closes automatically, as it was designed to do. Unless I'm running a winter mission, I'll open the radiator as soon as I take off, and leave it that way for the duration. Best thing to do, though, is always keep your eye on the gauges!
Hope this helps