I honestly don't get where all this nonsense comes from. Akame has no confirmed romantic interest in anyone. Girls who are close friends get pretty intimate in manga (such as groping each other in baths...). I'm a guy, but that doesn't really seem to represent real life and is probably done for fanservice. In fact, the closest thing she has to a love interest is Green (and she could have easily turned him down permanently by saying she was into girls). Finally, if you are going to make assumptions, given that Akame has no confirmed romantic interest in anyone, assuming she's straight makes more sense when looking at the statistics. However, I personally like that she has no romantic interests.
On a sidenote: the homosexual characters in AGK are very, very open about their sexuality (Bulat,Stylish, Mera, Suzuka...) and it's made beyond clear that they are gay. AGK has never handled homosexuality in a subtle way, why would they do so with Akame?
Don't get me wrong I don't care about her sexuality in itself, but it annoys me that people keep adding speculation like this to the wiki without any evidence. Enjoy your headcanon all you want, don’t go adding it to the articles.
There isn't really much more to say about this topic. All that's said in the manga is that Incursio is the prototype for Grand Chariot. However, that just means that both are the same "type" of Teigu (both are swords transforming into armor that increases the user's physical abilities). Apart from that, there is absolutely nothing to suggest Grand Chariot is also made from Tyrant. For reasons you already stated, it wouldn't make much sense. Grand Chariot looks different and doesn't have Tyrant's typical abilities such as evolving and camouflage. It also makes little sense that such a connection is never touched upon. Grand Chariot and Incursio are similar because Wave is Tasumi's foil, the same roughly applies for Akame and Kurome and their Teigu. Their's nothing to suggest any connection beyond that, and given Wave's character and Grand Chariot's design it makes more sense to me that it was based on some aquatic danger beast. That's just a guess though.
While I think the overall story could go rather similar early on, their could be some mayor changes near the end. My main example is the chapters were Mine goes to save Tatsumi (with the assistance of the rest of Night Raid). Thanks to Pumpkin and her feelings, she was able to distract Esdeath and kill Budo. Sheele, being someone who fights soley in close combat and isn't that (in-universe) agile either, doesn't have the skillset to replace Mine in this situation. And without her, the battle against Esdeath and Budo could go very differently.