I have a GTX1660 and the GPU usage is slightly lower when using Vulkan. No difference in stability or gameplay. 40 hours ingame and no crashes so far.
Have you updated GPU drivers?
For bases, primer and other rough work I use Winsor & Newton Foundation series. They come in large and cheap packs and last for 6 to 12 months.
For detail work I use Raphael 8404 series. They are around 20 euros per piece, but last years if maintained well.
Getting rid of the ancient finecast models was a welcome addition. Even the bio/pyrovore looks very unlike anything in the current Tyranid lineup. Also the Norn Emissary looks awesome. Maybe big enough to be a LoW. Definitely getting one of those.
The base markings are for weight class. 1 light, 2 medium, 3 heavy and a thick stripe for assaults.