The main thing is the animation packs OStim has pretty much all the old anim packs in SLAL (sexlab conversion) to be able to use. Any you have that are not can be googled on how to convert pretty easy stuff.
Here is my list of easy to find covers all the bases animation packs (mostly) including bondage devices (ZaZ)
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[Edit] Ostim keeps an alignment file stored somewhere. (I forget) There is a tool on nexus that you can load into MO2 so you can merge animation pack alignment files together.
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The problem is the smols in HPC are pretty smol so the petite and small animations are set for the default smol height so they kinda suck. I will probably do another edit to HPC to restore the scale to the default smol height since that is the easiest fix rather than redoing every animation.
[Edit2] I must say I just thought about the thing to mention on how Ostim in my research turned out to be the superior (imo) sex animation framework. Physics. Sexlab does not support The New Gentlemen which is a physics enabled cock. So my dongs sway in the breeze and can actually push open the orifices from my understanding if that was not animated in sexlab you didn't see it. That is why I took the time to Unlock Ostim and its addons for smols instead of digging.