1) The weekends isn’t the problem where there isn’t population, its the weekdays. The better idea would be to use double XP weekdays as a reason to play during the week, and not just on weekends. That being said, the idea as a whole shouldn’t happen. As you pointed at, the only bonus to levels is the “war” classes - If we double the XP, it will reduce the appeal to buy level boosts, and implementing things that further lower profits is not a good idea.
2) Once again, money can be bought on the shop, and this will reduce profits. If something was implemented to increase in-game income, it should be more ways to make/earn money, not just free double days.
3) War Veterans are meant for players who have been here long enough to get lots of levels, and be rewarded for that. The war heros are rewards specifically for people that buy level boosts - theyre not supposed to be obtainable by normal means. Once again, you mention war heros being the only thing levels are used for - If we make the requirement lower, it will diminish the desire to buy level boosts, since those classes are the main reason to buy the boosts.
4) Actually +support here - As long as they are all one-time uses. Personally, I think it should be restricted to only guns - not knives. Knives are special store items, and shouldn’t be gotten for free. Weapons that could be used for this are the old CW2 unused weapons.
5) This will end up with a server full of AFKs. Way back a long time ago when job income was super high, the server just turned into ‘who can afk the most’.