There are some interesting TFT 3.5" displays on the market today. These plug directly into an Arduino, but if this is an UNO then they occupy all the I/O pins! But if an Arduino Mega is used then there are more than ample other pins to use - both digital and analog.
There is also a couple of libraries which make programming the display relatively easy
- Adafruit GFX
- MCUFRIEND_kbv (what a kinky name!)
These can be used natively to address the display.
But I have re-written my popular OLED header (Oled.h) which provides functions suitable for many Amateur Radio applications - Bar graphs, Frequency, Date & Time, messages...
This is called TFT.h
All the info you need to use this header file in on my site M0IFA.me. Here you will find the libraries needed and a TFT TEST sketch (under UTILITIES) so you can try it out and learn how to use it.