First of all, welcome to the sight.
A stock XD 45 will have 2 things working against the beginner handgun shooter. A long and un crisp trigger pull, and fairly snappy recoil. Not the easiest handgun to start off with, but by no means a terrible choice. It's a reliable gun with good power and capacity and it's definitely a very effective gun with a little practice.
Anyway, a laser sight, depending on the type of gun and holster, will often not change the holster fit. As far as holsters, there are 2 brands I suggest. Safariland and Blackhawk. Any Level 2 or 3 holster from either manufacturer that looks good to you will work well.
To improve your target shooting, before you get a laser sight, there are 2 things I suggest. 1 handed, fast point shooting without the use of sights at up close targets. Rex Applegate made several notable books about training to do this. The most popular is Kill Or Get Killed, a book that a weapons enthusiast should read intently.
The other thing I suggest doing some of is 2 handed aimed firing, often called "modern technique" pistol shooting. I have not put so much effort into studying this method, because up close and under stress (sort of stress, I try to simulate adrenalin rushes by running really hard then engaging targets) I've found point shooting works better for me. Books about 2 handed aimed shooting are also available.
By the way, just to make it clear, I do think a laser sight is a good idea, I just suggest that you improve your aim a bit to make sure your basic technique is where you want it first. And by the way, speaking of the iron sights, a company called "XS Express Sights" makes some very easy to aim sights, and they are worth taking a look at.
There are many people here more skilled and knowledgeable than I am when it comes to hand gun techniques, and hopefully they will post soon with other pointers.
Hope that helps.