Thanks for checking it out. Like I mentioned, I work mostly on the hardware side of things rather than the software side, so I anticipated bugs and little things with the formatting and such. One of the reasons I opened it up for others to play with. I was starting to get tunnel visioned! 
Indents & Tabs
I'm not sure what you mean on the indents and tabs, though. I don't see anything on my end when opening the source code in any of my editors, even Arduino 1.8 and 2, and when viewing on GitHub. It all lines up evenly, and my tabs are all set for 2 spaces. The only time I'll use more than one tab is when lining up comments at the end of a line, and all my editors are set so a tab is "2 spaces". So I must be missing something somewhere. But that's an easy fix to redo all the indents.
Wire.setClock
The Wire.setClock values came from the display's suggestions of accepted values, but I'll make that fix to make I2C_SLOW = 50000 (50kHz). The one time I tested it at 10kHz it seemed to work, but I think that's because...
Wire.write() Delays
...the delay between Wire.write() was longer. I know it seems silly to do all that with the delays, trust me. But they were suggested by the manufacturer's examples I dug up, and initially I tossed them aside. However, every time I removed them or lowered the delay period, the display started to bug out and show junk, sort of like the display wasn't able to keep up. So I wrote it like it is now with the tiniest possible delay, just to keep the display working. But I already planned on fixing it, and it just didn't seem like it would be an issue if I left it as is for the time being while I toyed around with a solution. Though I didn't try it your way yet, so thank you for that. It's greatly appreciated help that seems to be working.
Serial.write() Delays
And I'll remove the RS232 delays as well. Truthfully, I added them because of the aforementioned issues I was having. I figured they were too small to cause issues, but just big enough to prevent any possible similar ones. But I'd rather not have them then deal with baud rate issues because of them.
Thank you very much for your time and help. I know I'm nowhere close to being a code guru god, but my heart is in the right place. I'm just trying to make something that'll help people 
Check back on the LiquidCrystal NKC GitHub repo, or Arduino Library Manager, next Friday for weekly updates. I plan on doing weekly updates on Fridays if/when there are things that need to be fixed or modified.
In the meantime, if there are any other comments, suggestions, fixes, and so on before then, either here or on the LC NKC GitHub repo's Issues page, I'll do my absolute best to get to them before Friday! 