I think it's a safe bet she already has an infinity stone. Hence the Myu-myu crushing and the fiery mowing down of Asgard. I'm guessing the Souls Stone since it's the only one unaccounted for and...well: Queen of Hel, Goddess of Lost Souls.
As for the tesseract: I note in several shots there are wormholes in the sky very similar to the one from 'Avengers', so I'm guessing Loki still has it and is lending it's use to the Grandmaster to gather his contenders for the games in exchange for...something? Also probably how he got Hulk off of Earth.
It could be, but I think Hela is meant to have that power naturally as a goddess or one of the eldest beings like the Celestials and Titans. I know it's a meme but viewers have created a list of objects;
T Tesseract Space stone
H Hela? Soul stone
A Aether Reality stone
N Necklace Time stone
O Orb Power stone
S Scepter Mind stone
H being Hela would fit the pattern. And finally have a stone that didn't turn out to be on Earth, or already in the posession of a known antagonist.
The skyholes...no one seems to be reacting to them and there are a lot of them all at once with no power beam from the Tesseract, I think the planet has those portals of their own accord and have been doing this for some time through their own technology. Looks more like the Aether's work...which is kind of bad if they're already coming together.