I'm a little confused about your first question- the pic you show has the yellow stickers in the 2nd group down on the left column. Does your sticker pack look different than this, or am I missing something?
Also, is it right that all Hero's get the purple upgrade as their one upgrade on the single blank bar? Is that what the purple chain icon represents?
This is correct. This group of purple stickers appiles to the hero itself, in the slot on the side of the card with unit stats and oriented horizontally. The chain icon is found on some command/equipment cards as well, and represents an equipment attachment, as opposed to single use equipment.
Hope this helps!