-are there base stats for each "race" (trolls, ogres, dragons etc) ? (and if yes where are located?)
CoreMonsterUnitTypes.xml
-if the above if no can i add general stats to each unit or im bind to use the per lvl setup?
You have to use the milestones, or you can give them traits that increase strength per their level
Note that the milestones are ONLY used to set the stats of a unit AT ITS SPAWN. They are NOT used to update a unit's powers when it levels up. For that you need to use equipment or traits with modifiers that increase based on level.
Keep in mind all units in the game gain hitpoints accuracy and spell resist as they level up.
-can i change the party settings for lairs?
Yes, find the right lair in CoreGoodieHuts.xml. You'll find the XML you need by looking at already existing grouped units such as Mite lair: <UnitGroupingType>UnitGroupingType_Group</UnitGroupingType>. Note the group type is set in the monster lair for this scenario.
- is there a trick to start a game with peculiar settings?
We do not have map editor access. In E:wom we used that to test our new goodiehuts and quests - simply make a map and put it there. But the workshop is not yet released for modders so we can't do it in FE yet.
One way to test them right now is to simply put their <Rarity> very high. Then your map will be filled with that kind of goodiehut.