How many battles are planed for this campaign? How long is the campaign going to last?

From your story, it sounds that you have installed the game correctly, as it appears that you can start it.

If you want to play singleplayer, you should go to the multiplayer tab, than start local server in coop mode. Then you can play many maps with bots. This may sound unintuitive and it is, but it gives you more options on teambalance and difficulty, as the original standard bf2 single player tab.

Is there a detailed changelog? I am wondering, what other details got addressed? Balance & bug fixes?

Thank you devs and the whole community for the joyful last 10 years and more to come.

I personally love the game as it is. It's relatively simple playstyle. Just spawn and start. It's scenario. The deadly gamestyle. FH is the only game I know, which somehow manages to combine a realistic feeling with an arcady, fast paced gameplay (not negative, this is what I mean with 'simple playstyle'). No other game has this unique combination. Of course, this combined with air, land (and sea) is awesome.

If I could change things in this game, It wouldn't be much. I love to be a squadleader in this game and the spawn mechanics inherited from vBF2 are extremely nice. But there is one thing: while in vBF2, you have medics and can be revived, you can't be in FH2 (which is fine). However, this means that per team up to 9 people are just relegated to hide and NOT to attack, because else you loose your spawn. And everybody hates his squadleader, who always is killed. Also as a squadleader you can rarely man any defensive structure. Again, nobody can spawn. This doesn't fit the game. While certainly people pretend to be role players, the leading in this game mainly comes from the spawn point location of the squadleader. He hides and this decides the direction of attack. Nothing else.
Personally, there are two things: I either would love to see more of the spawn half tracks/vehicles. This means that defending team has to destroy the spawn vehicle, which adds another gameplay element. But I personally would favor the introduction of rally points, similar to PR or in the campaigns. In the campaigns it works wonderful and an important gameplay element it is always to find the enemy rallypoint. This way the squadleader can take a more active role, he can fight. Spot for artillery, and actually go for a flagzone without worrying about being killed. 10 players more to fight on the server, who wouldn't want that? I mean this can be balanced. Limit the time of the rally point, e.g. 5 minutes. Limit the minimum distance to flags. Both exist already in the campaign. And if you don't want to have the whole squad pop from a pile of bagpacka/a radio, make the rally point only a fall back option for the squadleader. So only he can spawn, when he dies, but the squad still spawns on him. That is the only thing that is bothering to be a squadleader. YOU don't have a spawn, a fall back option, when you are killed. The rest of the squad has. And it is you.

PS: That is just my opinion. My dream.

Something like this, is what I thought.

Because shouldn't the existing 155mm shaped charge shells already powerful enough to bust a tank? Looking at the Russian SU152 even a big HE shell should destroy any tank. Therefore, I was wondering, what such a shell is even for. 

What is that? Some pz3 prototype with Schachtellaufwerk?

Now that's going to speed up face modelling for FH2. Just 2 polygons and a little texture.