I tried a 2h-sword lacerate build first and then went to kinetic blast wander.
I know that I fucked up picking my first build, but that is the point. I am a medium-core gamer these days. I am way more than casual, but I have a job and kids. I'm more than happy to grind for a goal to a point. The fact that I picked a solid build with a known build path and am stuck at early mapping to grind currency to buy better gear or fusings to try to 5L or 6L my QotF is a huge problem for the gear. Added on that the game is so complex to make significant smaller upgrades impossible to determine without thousands of hours of experience or more currency to test with and you get a situation where I don't care when I'm this far behind.
2H sword Lacerate is probably "fine". And by fine, I mean you should have been able to work your way into red tier maps easily. It's not a build I would have gone with, but I don't particularly like Lacerate nor 2H builds(too slow). I think sticking with that build would have been fine, or based on what you wanted to switch into, probably could have been done with a modicum of regrets.
As for your situation with which upgrades to get first...that's a tough one. Unfortunately, that just comes with time and experience. If you aren't already, PoB is extremely helpful in this regard. When I plan a build, I make 2 profiles in PoB. 1 for level 90 with "average" level gear, nothing that should be too expensive unless it has to be. And then another at level 95 where the desired affixes are turned up and maybe some more uniques slotted into the build.
You did make two mistakes though. Switching into Kinetic Blast before stockpiling enough currency. For some reason, despite no changes in mechanics, KB is extremely meta. I'm selling shit tier Pisctor's for 5c, it's unreal. Maybe it's the MTX, maybe it's Underground Sea(probably), maybe it's that every streamer is playing it for their farm build. But for casuals, I would not recommend it. KB is frustratingly dependent on density and map layout too. If you're not doing a shaped map strategy, I wouldn't recommend KB even if you're hardcore.
Trying to 6-link your QoTF with fusings. That's just asking for heartache. If the 6-link is important and you don't have the currency to support failure, I just live with a 5L until can straight up buy a 6L. And I don't even 5L my gear with fusings either, I buy those directly too. What's the average cost to 5L, 150 fusings? That's 100c! I can find a 5L chestpiece for much cheaper than that.