ooowwwwwwwwwhhhhh Look at the Newbi!!:D
To maintain "E", avoid doing high "G" manuvers. The harder you pull, push the stick, the more energy you use. If you make a run on an enemy, make your pass, and then pull your turn as tight as you can to get another run, you've burned half your "E" and speed is now down to 150 knts. If on the other hand you make your pass, pull up easy and make a big wide turn to get back in for the next shot, you'll still be at 300+ for speed with a bunch of "E". The only time you want to get slow in almost any plane is for your landing

Climbing.... well what can ya say, it takes time. After you launch, set your heading, and hit "ALT x" This will put the plane in auto climb, and for MOST models its the best climb rate for all the planes. Some people like to level and use WEP for a min or two then go into auto climb, depending on the plane.
Diving..... drop your throttles to 0, if you need to slow more, give it hard rudder to one side. If the plane starts buffeting.... bouncing around...pull up, and climb to burn more speed, then start dive again. Buffeting is the main signal that your plane is about to start compressing and you are going to lose manuvering control. Its better to call off a dive halway down, and try again, them to just "lawn dart" your plane.
Good Luck and welcome to Aces High !