sims 4 crashing when I try to test CC ?

You should transfer weights from another pants, not from full sim body including head etc. Your weights and uv_1 reference mesh should be similar to what you have, so bell bottom ea pants should work.
Because you transfered weights wrongly your mesh was broken and crashed. In blender join your mesh together, use arrow down next to weights list and Delete All Groups so you have empty list, append proper reference mesh and transfer weights from it. After transfering in weights menu use options: Clean (All Gropus) and Limit Total (Limit to 4). Then cut your mesh back as it was before and set proper cut numbers to them so they match base you used to create package.
Depends what you mean with go over shoes. If you do not want to glitch your pants with higher (ones with platform etc) shoes, then not really, you would have to move them really high to suit all shoes. If you want to hide high shoes under your pants, then you should have your mesh with few cuts as you have now. Only thing is that some shoes hide under and others go above, as far as I know it depends on layer number you have in Region Map set to particular cut and your pants should have it higher than shoes (example: pants calf cut is 400, shoes 500, then shoes go above pants, but if shoes is 100, then they hide under). Also remember that cc shoes are often made on one mesh group and they are not going to work with your cuts and will glitch

Hi. Transferring the data from cc is not a good idea ( in a sense that cc creators do not "know better" than maxis developers, so it is unlikely that the result will be better in any way ) and wont change anything ( if your reference doesnt crush the game, what you transferred from it is not causing the problem, so maxis pants are not the problem here)

The problem here seems to lie in the fact that those bones from all the body you imported the first time corrupted the package. So you just need to clone yfBottom_PantsBootcut again and import the blend there.
When you split the mesh into multiple meshgroups, all the bones in Vertex group list stay, even if they do not affect it. Sometimes there can be too many of them, so it is best to always remove unused ones from each meshgroup with this free addon. So its not that the whole body you used initially is bad or unsuitable as a reference, it just has too many bones foe a single meshgroup
A few unrelated things:
- if you want to make an empty specular, this is not really the best way of doing this. If you have a beta version of s4s, just click on Make empty and it will create the correct version;
- it is best to delete bottom.001 from under the rig. The game doesnt like when you modify the rig or what is parented to it in any way, so if you have to, it is best to undo/delete it in the end