I have once considered some STM32L4 for paralel LCD: tldr: I strongly disadvise. Save ton of time and hardware money, get mcu with ltdc and enough ram onboard and enjoy the life.
Precisely, I used FMC, no external memory. Targeted in magnificent, unbuffered 8-bit color space. Thing turned out to have to have risky, close to margin timings, depending on internal bus clock and internal FMC write fifo and timings trims. Required external gates, timers for sync pulses and wasn't sure if lcd would approve of not ideally synchronised pulses. Plus a lot of soft to control, DMA's 16bit item counter wasn't enough, bla bla. Generally I dropped it, too many nasty contraints and potential, fatal pitfalls.