You don't need to have multiple layers to use a mask for each separate body part.
You can have a single track matte layer with several masks on it, one for each body part. So, you'd have one background layer, one track matte layer, and one foreground layer. That is how rotoscoping is typically done.
(Sometimes the track matte layer is a precomposition, with a matte built out of a lot of pieces with a lot of layers within it, but that's more advanced.)
Maybe this mini tutorial will help:
The stabilizer I was talking about was NOT warp stabilizing. It was AE's point tracker set to stabilize. Watch the video about 3 times and you'll catch on.
One more hint, Don't waste any time on a single frame that is not going to need to be rotoscoped. Overlay your explosions, then trim your layers so that you are only masking what needs to be masked.
This also applies to using AE's new and vastly improved Rotobrush tool. Don't waste your time masking anything that does not need to be masked. Most beginners will roto a 30 second shot carefully cutting out an entire actor when they really only needed to mask about 60 frames of the actors left side and hand to pull off the effect.
Good luck. Roto, even Rotobrush, takes a little practice, but it's not hard and it doesn't need to be time consuming.