Hehe IP will have a blas when he reads this....
Ok, about your gripes: You've made through some of the more frustrating missions, so the ride shold get a bit smoother from now on.
1. Congrats on taking out all fighters. An alternative (and easier) way would be to severly damage one of the Narn transports, which will cause them to surrender. This can be done quick enough to stop all Frazis before they pummel the Centauri transport.
2. The asteroid field density depends on your difficulty setting (the higher your setting, the more rock get thrown at you). The mission is balanced for "Easy" setting IIRC. I couldn't finish it on "Medium".
3. The Asimov transport is supposed to blow up, it's part of the storyline. There's nothing you can do to save it. When it's gone kaboom, you have to defend some of the escape pods though. Target an escape pod and press "g" to target its nearest attacker and focus on killing that Zephyr, rinse and repeat. And you have to survive the mission of course
I hope that helps a bit. Direct all your blame towards IP Andrews, since he wrote the missions ;)