Check the file sizes of the .pcs and .pac. The .pac should be uncompressed (which means that they should be larger in file size than their .pcs counterparts).
It's probably because no one knows what exactly is causing the problem.
I've heard (well, more like read) that some of the common files (common, common2, etc) have MotionEtc files in them and replacing them might prevent the freezing.
Open the Calculator application on your computer. Make sure you set it to "hex".
Type in the character ID no. Add 30 (or 68, if you use the second code) just like a regular decimal math problem. That new value is what you would plug in to XX or YY.
Yes, if you use different movesets, you will desync.
A solution is to not use them at all, or for everyone in the match to have the exact same movesets (ie all players must have the Cloud moveset for Ike if one player chooses to be Cloud).
Simply, Touhou is a "shoot 'em up" game (call it "danmaku", or bullet hell) for the PC. It's an EXTREMELY popular series made by the group, Team Shanghai Alice, which is composed of one man god, ZUN. The gameplay features you having to dodge enemy attacks which take the shape of patterns formed by bullets. ...But a video may be more worthwhile than an explanation.