I am running skitarii regularly at the moment, and they make... ok... allies. They have squishy/crunchy untransported infantry but are really deadly at 18 inches (running vanguard) and have excellent snipers who can shoot pretty much the whole board.
My games lately have been imperial knight, skitarii, Grey Knights, so three books. I would advise getting to know each army first, so perhaps play some small games with each. This way, you learn the armies and don't need to crack three codexes all the time to look for rules, which will really slow you down. Once you've got a good memory of each army though, I highly endorse it! You may notice I'm something of a guard fanatic, so with their artillery formation from Mont'ka, a space marine formation and a skitarii detachment or dominus maniple formation, you should have a good army at 1750 - 2500 points!