I typically have powder in a small plastic baggie (whatever it came in) plus a desiccant pack inside a labeled black mylar bag. The desiccant pack doesn't come in to contact with any powder.

Heat sealing and vacuum sealing are different. It's possible to heatseal mylar using something like this, though I never have. It's not possible to vacuum seal them. I keep desiccant in each bag since they're not sealed, just ziplocked closed.

I don't recommend putting a pack directly in with powder because you tend to end up with a large amount of product stuck to the pack. I also don't see any extra benefit over having it within the same ziplocked bag. I've never used the raw desiccant beads, that was a suggestion from the comments that I added.

I'm not familiar with that particular scale but it says it measures to the milligram so it should be fine.

The gemini-20 can measure to single digit milligrams, not just in multiples of 10. When I said that it shouldn't be used for doses under 10mg that's because being off by even a small amount in that range can be a very large relative change in dose. E.g. if you're trying to measure out 8mg and the scale is off by 3mg then your real dose could range from 5mg to 11mg. For chemicals active at low doses that could be a huge difference in strength of effects and as such volumetric dosing should be used for safer and more precise dosing.

Attempting to add powder to a scale 1 or 2mg at a time can also introduce inaccuracy as sometimes the scale won't detect very small differences. If I need to add just a very small amount then afterwards I'll either lightly tap the surface with a microscoop or lift the entire weigh paper and place it back so the scale measures the full weight.

Here is a recent comment of mine where I briefly describe my process for weighing out doses.

Hope that helps, if I missed anything or you have further questions lmk and I'll try to go into more detail.