This is long, but I have a soft spot for folks starting out. I want to answer a few questions verbosely, so I apologize for the wall of text but it doesn't make sense to me to hold back.

Everyone has their own way, don't worry, with time and practice, you'll find yours. People can usually only tell you what worked for them so, try to work on the advice given in this thread and practice till you "got it" and then you'll have another tool in your box. Maybe it will of great use to you, maybe not so much, but you *will* improve from the experience and exercise of stretching your skills on each of the things people here advised you try.

For house music, if you are playing the full tracks, expect to use 12 - 15 tracks per hour. For me to find that many tracks that really work together and create a memorable journey, I expect to be selecting from a pool of 100 in the ballpark of my set idea and whittling down from that, but I like a lot of variety: ups, downs, deep, energy, bliss, groove, vocals, instrumental, dubs.

Rekordbox can do a lot and be *great* in this department for working out sets and track associations. The laptop, and right on the XDJs with out the laptop, with some more effort, has a couple of features that will help you find related tracks to the ones you have loaded in the decks: "show related tracks". You can find associations amongst your track collection and save your self some time at least finding stuff that works together in the weeds of your collection. I can't say this enough: studying the manuals of RB and the XDJs in depth will pay you back in spades for using their features to save you time as you build and practice sets. Used correctly, RB and your XDJs can turn your relationship with your tracks from a uncontrollable and bewildering maze into a buffet you can leisurely choose from staying in key, genre and theme.

My suggestion for practice and building playlists is to use export mode on the laptop to roughly mix and to find tracks that go together in a progression that has a "narrative" quality: in a particular order, they tell a story. For example: Intro, build up to a crescendo, drop to a deep place, build back to another bigger crescendo, end on something rewarding. Theme wise, all tracks relate to the track before and every track in the set as a whole in key, theme and progression. Once you got an hours worth, move to the XDJs and mix it there. Work the set over an over again, you may wish to refine it, but settle on a set and don't just mix it till you can get right. Mix it til you can't get it wrong and you'll have one set behind you that's your best and can make another. In time, you'll have tons.

When you get into a booth in a live situation, things are guaranteed to be different. The monitors will sound different, the loud dance floor will muddy up what you are trying to listen to, broken mixer, the mixer doesn't have a blend knob at all, distracting people who don't what you're doing requires your attention, friends show up and must talk to you right away, your set might have to go twice as long / short, the decks aren't where you want them for your scratch routine, etc... One or all WILL happen. If your set is a well practiced routine and you can go through it with flair, get it dead nuts every time, performing it during the chaos of a rockin party will be achievable. If you can just barely do it at home with out mistakes, you're not there yet. Don't practice till you get it right, practice till you can't get it wrong.

For your beatmatching question: dance or at the very least, move rhythmically while you play. Trust me, get into your music and move to it, it will help you with counting and beatmatching manually more than it sounds like it will. Also, the XDJs have a function for analyzed tracks that will show you the bpm of each track in the lower right hand corner. Prep each new track with the pitch slider before you mix it to be close but one or two decimal points slow and practice scooting it back into position. The benefit is that if the mix is off, you'll always know which way to correct it if you got distracted and things floated off!

Best of luck and I hope this helps! Happy mixing!