[General Questions and Answers] Android#:
Finally, some very good news for people like me who are stuck, figured out a way to root and install Xposed both :) Please give credit to Magisk and Xposed developers listed below.

Root:

Root this phone while it is running the FTJ152D marshmallow stock rom using the Magisk guide here:

https://xdaforums.com/apps/magisk/official-magisk-v7-universal-systemless-t3473445

Follow the "Via Magisk Manager (Only support v14.0+): ... " method to install the magisk manager and the .zip file right through it. It patches the boot and makes a patched boot image that you can transfer to your computer and then rename it to boot.img and replace the original boot.img in the FTJ152D MM rom folder. Then use the SP Flash tool, load the scatter file in the rom folder and the 'Format all + Download' option in download tab (it will give you PMT error if you try to just flash the new boot.img alone). Hit the download button, turn the phone off, and connect it to the computer via usb. Everything else should be straightforward but if any issues, ask here, and I will try help if I can.

Xposed:

There is no touch support to make custom recovery work on this phone yet and the only custom recovery i got to work was an old version of CWM which behaved same like stock recovery and refused to let me flash zip files. The workaround I found that worked was 'Flashify' on Play Store. Now that root is working, flashify seems to work (tried Flashfire too but it just hangs and phone freezes). Follow the steps below:

1) Download and install the latest Xposed Installer Apk from their page.

2) Download the appropriate xposed zip file (SDK23 ARM-64), version 89 worked for me. Use Flashify to flash the zip file. If any issues come up, ask here and I will try help.

Official Xposed post is here:

https://xdaforums.com/showthread.php?t=3034811

This post is also very helpful:

https://xdaforums.com/showpost.php?p=67696847&postcount=2

All credits go to the respective developers for their work, including [MENTION=4470081]topjohnwu[/MENTION], [MENTION=4419114]rovo89[/MENTION], [MENTION=719438]mGforCe[/MENTION], [MENTION=260994]SolarWarez[/MENTION], [MENTION=3303102]MaArCiN074[/MENTION] and others. Don't forget to thank them.

I also have been able to replace the demo mode logo with logo that was in the partial stock rom dump and will share it soon.

IMEI issue:

After gaining root and installing Xposed, a number of apps can help to at least temporarily get the IMEI written to the phone, that lasts till factory reset. One issue that people like me who installed the FTJ152D MM rom is that the bands in the phone are now based on the Japan region and almost all the frequencies and bands needed for phone to get 3g and 4g signal are disabled in the phone. From researching about this issue I found out (I may be wrong but that's the only information I could find and the bands that are enabled seem to confirm this), is that the latest mediatek chips come with all 41 bands and the phone manufacturers and operators disable or enable bands based on their regions and preferences, so that this phone, FTU152D is probably the exact same hardware as the FTJ152D and the only difference is the software which disables and enables the bands based on the baseband version of the rom. This is a problem for ppl like me living here in U.S but the enabled bands may be fine elsewhere. There is no way to change the bands as they are greyed out when you go to modem information though 'Phone Information' section (apps like 'Advanced Signal Status' can help access it). It doesn't allow me to select and enable band 4 and 12 as these are greyed out (but these worked before with stock rom, so I know the hardware supports them just the baseband version is wrong now).

Anyone know or can help get the right bands working, or have any hints to point me in the right direction, please post here. Thanks.