Hi Duc,
Personally I don't think you were wrong in your approach to replacement; do it all at once and get it over with. There would really be no reason to expect a problem.
You mentioned using the alcohol to loosen the battery adhesive; did you do that just to try and improve your odds of success, or because the tabs broke off and you were forced to pry out the battery. If the latter, I'm wondering if there's any chance a flex cable under the battery perhaps got damaged in the course of getting a stuck battery out. Just one theory.
Personally I am skeptical that getting isopropyl alcohol on the logic board would have caused problems; I mean, people soak boards in the stuff after they've been exposed to water; the whole point to it is that it evaporates without leaving any residue, especially the 99% stuff you used. I wouldn't spend any more time on that issue if I were you.
Other than the possibility of any flex damage, you'll want to double check the lightning port and battery connectors on the logic board. Use a magnifying glass and a bright light and look for any bent or broken pins; in addition, check around the connectors for any small components that may have been damaged or dislodged from around them.
If you still haven't found the problem, try to isolate it. Try disconnecting other components and see if it has any effect on the boot process; in particular the iPhone 7 had a lot of problems with the front camera assembly where those would frequently cause boot loops, so try booting with that disconnected. If not that, try as many other connectors as you can; rear cameras, wireless charging coil, taptic engine, etc. If anything changes the behavior that's likely your culprit.
One thing that is somewhat confusing me is your statement that you removed the lightning port assembly without removing the motherboard. I'm curious how you accomplished that since part of the flex cable runs underneath the logic board so I'm not clear on how you got it out with the board in place.
Anyway, give some or all of those ideas a try and let us know what you find.