Always use binary, but if the device is not reachable at all there is a larger problem.
All the instructions that you've linked in this thread are for the 4A Gigabit with a MT7621 chip. Who's instructions are you following for your 10/100 MT7620 model 4?
I'm not following any specific instructions, I only so far did, connect router to laptop with ethernet cable, all other network WiFi and all disabled, press and hold reset button while powering on, LED flashes orange, then I run tftp 192.168.1.1, that's all I did, nothing more nothing less.
Can this be done with a Windows VM? If the windows route is easier?
I think I fixed it, I fired up a Windows VM with bridged connection, downloaded that tool TinyPXE server, and grabbed a image for my router from internet, and flashed it. I can now login to 192.168.31.1 it opens the Xiaomi Admin page now.
Can someone provide me proper installation instructions for OpenWRT, as I want to use OpenWRT, there are snapshot version available for my device here - OpenWRT-Snapshots starting with the name xiaomi_mi-router-4-
Check this out.
This is not for the model I have, I have Mi Router 4, the link you shared is for Mi Router 4A.
My bad, the Xiaomi naming is really confusing.... 
Updated link 
There are no instructions on the link you shared, all are for Mi Router 3. No instruction to enable SSH on Mi Router 4, or anything.
In that case you're pretty much out of luck. Googles your friend....
I have stock Xiaomi ROM right now, on the router, not OpenWRT, how will those instructions help me install it? Also they are for Mi 3G, I think now that Mi Router 4 is supported there should be proper instructions available for it too.
Out of curiosity,
why not use the OpenWRTInvasion script again, then redo what you did, without the typo ?
I can, but I want to, if possible do it the official way, there is always something new to learn, and I want to if possible 
@apoorv569 can you help with more steps of how you did to fix your box because I have the same problem and I can't find a way to fix it
I basically followed this video guide - https://www.youtube.com/watch?v=VxzEvdDWU_s&t=267s
If you have a Windows machine, you just need to install the tool he mentions in video, connect your router to PC in TFTP mode and flash the stock ROM (you need to have it downloaded before starting this process) for your router.
In my case though I didn't had a Windows machine so I fired up a Windows virtual machine using VirtualBox, and changed the network settings of the virtual machine to be bridged with the host system, and then followed the same video guide I mentioned above as if I'm using Windows.
Hope this helps.