The F is my second favorite 109. Like Baldy says, watch your dive speed, it gets tough to pull out of dives over 400 or so. You can trim your way out of a dive if you have enough alt though. Learn to back off your throttle if you're in a hard dive. Get close to shoot, 300 or less, 200 or less optimally, and the one 20 can hurt. It climbs well, especially on wep, try to keep fights vert against most opponents. You'll want to be on and off flaps frequently, over the top of vert moves as you get slower into turns too, you'll have to figure out what works best for you there. It can turn, and turn pretty well, and it accelerates well to boot. I like to fly it like a KI84, and sort of like I fly my K4 too. You can really surprise some people in it once you start to get a feel for it.
As for your second question, keeping in mind that I'm not really very good...
Are you talking about going into this merge in a co E situation? It sounds like you're possibly misjudging the bad guy's E level going into the merge. I try to get below the baddie on the merge, then lead immel so long as I don't cross directly in front of his guns. If you're pulling lightly and making it a big fat immel, you really should have more E than him at the top if he was pulling hard. You might also be very co E with them but they're just better at floating the plane around near a stall. It's hard to say without film. Again, keep in mind that I'm not that good at this stuff yet.
If you see me on, feel free to holler at me and I'll happily hit the DA with you to work on that kind of thing though. Good luck.