1.). I’d pick any major brand and variety first, then shop for the best price. If you need a slow cure resin for a single deep pour, then find that product which is designed for the pour thickness. If you are doing multiple thin pours—perhaps because you are embedding items that ‘float’ in the resin, then you’ll be able to use resins designed for thinner pours. These set up faster because their reactions are hotter, and would be too hot if used for a deeper pour.
The major brands like System 3, Total boat, West Systems, MAS, Alumilite, and others, offer products tested and tailored to specific project requirements. These traits are well documented and products should be reliable. It is worth a few dollars more.
2. Almost all epoxies are filled with re-actable chemical components, and have close to zero volatile organic compounds. That doesn’t mean they have no smell, just that the aroma is not from organic compounds (usually petroleum derivatives) that are volatile, and evaporate easily.
The big exception to this would be the penetrating epoxies which are thinned by adding a lot of solvents. These are designed to soak deeply into rotting and punky wood. When the solvents evaporate and the resin hardens it becomes harder than the original wood, and all moisture is sealed out so further rotting can’t happen.
3. No. Not naturally. If you want a matte finish theceafiredt