afaik the xdm in 45 acp hasn't been released yet. start local. check the classifides on this site. also check your local texes state forums. the problem with buying used online is you can't look at the gun and inspect it in person, and by the time you pay shipping and transfer fees, you would have been better off buying new. buying online is great for rare or discontinued guns, but for an xd, of wich there are thousands of, stick to local.
there is nothing wrong with a 1911 for a first gun, and can be found locally used for about the same price as an xd. another option for a first gun would be a 22. cheap ammo, doesnt scare away first time shooters, alows a shooter to relax and learn the fundamentals of shooting and owning a gun without breaking the bank. used ruger mk2's can be found all day long for around two bills. hope this helps, good luck.