I'm also doing the 'many months of dipping in and out of learning' thing haha, bought the game during steam sales.
I remember playing that mission a few months ago. At first it puzzled me until I realised they can't hit you at 20000+. I can't remember everything in the mission but here goes:
If I recall correctly the mission starts you off with 4 mavericks(?) I think there's 6 bunkers right, so after bombing the first and second bunkers from high altitude, you can jettison the rest of the rockets and bombs, climb, and just take the bunkers out with the mavericks, ignoring every single threat.
One thing that the mission doesn't explicitly explain (I think?) is that the enemy controls the river and everything left of the river. There's no defences or anything to the right of the river, except in the towns further ahead which may have manpads sitting in the town (I distinctly remember being launched at there and seeing the missile hit a building lol). In my opinion you should have easier access to this fact. I'd take good note of this and use the right side for your ingress and egress routes, pulling hard away from the target/split s after each attack.
There is this long range sam to the left of the river. It's pretty stupid. It will launch a billion missiles at you as you head in its direction but it's max range is just left of the river, so as long as you stay right of the river as I said it's not even a threat. Honestly though why would a long range sam fire at ground attack aircraft at that range, lol.
I did try a low alt run one time, staying lower than the trees. I was planning on using rockets and guns but they dont seem to do anything against the bunkers. Need bombs or mavs. Just jettison the rockets altogether, they are useless. They're CAS weapons, I don't see why i'd ever take them on a mission like this in the first place.