300 is a very small army. wait until you have at least 3 cities and build up to 10k troops if you are new to the game. the temp camp huts are adjusted so that you will get a quest if you should be able to survive (This only takes player experience points into account so its very inaccurate at judging your current strength).

adventurehuts, you should only try the abandoned mines as they are the easiest.

merc camps, these are fought over for control by other players. so without being part of an order or an vassal of a member of an order, you are most likely not to be able to capture or control one of these places for long.

remember, no matter how how weak these places are, other players may visit them too so...