Im guessing you guys combined all the options into "mod options" now, but my question is, where did the option go where you can set "enable terrain advantage in battle" or something.
In the mod options screen. Just scroll down.
How can I make "Battle size" larger, over 150? 
i don't think you can get a higher battlesize than 150, but if you could, it would be very laggy
You get the battlesizer mod from the forge. It is run external to the game and can set your fights up to a size of 1000 people (very laggy unless you have a high end computer). If I remember right you also need to set that same number in the Floris mod options once using the battlesizer mod.
You can find it here in the Caravanserai:
Warband Battle Size ChangerWhat affects lords armies size? Is it scaled to my level, renown or they increase independent?
Your level, yes. And your campaign difficulty setting. But also their leadership skill (set in the troops file) and their renown (set at game start, and only increased by winning tournaments, being marshal and hosting feasts). Also, they get a bump if they are marshal or king. And a bump for holding towns/castles. And the total number of fiefs determines how much coin they have to upgrade their troops or recruit more rapidly when they lose a battle.
Is it possible to recruit manhunters some other why then recrutingthem from captured after battle?
Nope.
1 more about lords returning from exile in mod options. With this disabled exiled lords will dissapear forever or they just won't come to me asking for becoming my vasals?
With it disabled, it will be like native--once a lord makes the full round of kingdoms they will be exiled from Calradia and disappear forever.
And whats the best way to make a town gain prosperity?
The other thing you can do is lower taxes via your diplomacy staff members if the town is under your control.