1: I'm not a big tanker, so use with caution. There still are hitpoints, but they don't really matter afaik. If a shot penetrates, the tank is usually destroyed, sometimes it might take two shots. Tank armor has weak spots and is based on real life values, but I don't think it is as accurate as ROs model, due to engine limtations. There is, for example, no way to disable the tracks or motor of a tank. Also, the tanks are not multi crewed, but since you want to mod the game anyway, you could add that.
2: Yes you can, but it's quite hard.
3: About realism: we have a one hit - one kill system for infantry, iron sights, realistic jump height, sprint speeds etc, but the mod isn't hyper realistic like for example Project Reality. Some features from Red Orchestra like setting up MGs on sandbags or proper bayonets can't be implemented because of engine limitations. Other than that I'd say RO and FH2 are on equal level of realism. The weapons are all authentic and historically correct. There have been made no changes to the AT Rifles to make them more powerful (like in RO).