We already know the worst outcome that everyone considers in universe, Empty Night, the destruction of all reality.

As long as they are on the same page.  Mab was willing to have her child killed because she was infected, I'm not so sure Harry would do the same thing.

If Maggie were about magically nuke Chicago(which was what would have happened in Cold Days if Maeve wasn't stopped), I think Harry would make the hard choice . It would break him afterwards but he'd choose the millions of innocents over over one person committing an evil act no matter how much he loves her.

I don't see them ever being a lovey-dovey couple but more "friends with occasional benefits" who work together.

I think Lara will bail Harry out of various situations and require sex as compensation when she doesn't need something Wizardly at the time. We've already seen Harry start to feel the pull of debt obligations through his mantle. Lara will use that to her advantage in their personal and business interactions.

Depends on how they work. Does the Angel loan its Grace to the blade?

So far, the Angel and the Sword have not been portrayed as being two distinct things. The Sword is a tool fused with the Angel and through it the Angel gives the Knight access to some of it's heavenly power. But the Angel is in control, not the Knight. The power is withdrawn as soon as a Knight begins to misuse it. Angels often take further control, such as Murphy's speech in Chichen Itza and Michael's in Marcone's vault.     

I think part of freeing Thomas will involve Papa Wraith's death.

I don't think Thomas' next role is as KotC but as the next White King. The trick will be having Papa Wraith take the fall for the Svartalves assassination attempt and getting Thomas cured tied together in an impeccable story that also implies that Lara was the mover and shaker behind the scenes.

If Lara and Harry can make it seem that they've been allies for a longer time, then typical White Court paranoia will sew just enough doubt that Harry might be acting and is secretly a masterful deep schemer. Don't laugh, Lara was half convinced of this at the end of Peace Talks and she has more inside information on Harry than 99% of the supernatural world. From the outside, you can make a case for Lara and Harry being a team since meeting on the movie set.

The timeline actually flows pretty well for a conspiracy theorist.

Harry and Lara meet on the movie shoot, She defies her father's orders to kill him and works with Harry to perform a palace coup.

It's Harry she calls upon to defeat the first real threat to her power in White Night. He doesn't leave with the rest of "his" allies but accompanies Lara back to the mansion.

Harry is called in to deal with the Skinwalker and the attempt to restart the war with the White Council in Turn Coat and she delays her departure until she can personally speak with him.

Harry is the person who makes all her introductions in Peace Talks.

And now, she engaged to Harry, the Winter Knight, just as the White Council kicks him out. His role as her spy in the White Council has reached it's end, now they will inveigle the Winter Court together.

The next step is to finally put away Papa Wraith and install their pawn/co-conspirator Thomas as the White King while building their powerbase.

Wizard of Chicago comes next. Harry and Lara spend the year before their marriage getting him in with the Chicago social scene.  Operating a new magical organization will be a perfect cover for their secret activities. It won't fool the Accorded Nations but it'll do a fine job against mortal authorities coming in after Battle Ground. A big flashy target that does authentic good works will build up good PR at the least. Drop a few juicy secrets for the Men in Black to discover and they'll inevitably take the easier route and focus their attention there and away from the really important stuff. Pretty good improvisation to cover the completely world changing event Ethniu caused

The Immortals will know this is all nuttier than an explosion at the the Planter's packaging plant but for the majority of the Supernatural world Looks like a master plan between the Queen White Court schemer and her young new Wizard lover.

After the wedding Harry will no longer have protection from Lara. The wedding vows are a spell that removes true love protection. See Something Borrowed for confirmation.

I haven't read that one, but in any case that true love protection is really not the obstacle that people think is in practicable terms.

Mab can order Harry into bed with any Winter fae lady other than Molly to break it and Justine had no problems finding willing threesome partners to help with Thomas so I really doubt Lara couldn't find one or two just lying about(both literally and figuratively) to help out.

And since consummation is part an old school marriage, Harry is dutybound to accept whatever option is chosen at least once which is all it takes to cancel it.

The alliance with Mab will make Lara stronger with the rest of her Court. Harry won't be a live grenade, but more a machine gun emplacement that just makes her defenses that much tougher.

The Swords aren't on loan. They are there in partnership with the Knight and always aware of how they being used. Mavra didn't try to use the Sword at the party, she just traded it to Bianca. It was vulnerable because it wasn't in the possession of a Knight and could be broken but I highly doubt it could be corrupted.