4-8 Ah seems good. “6.5 Ah 3 hours @ 50 W”
FT857 RX current draw is advertised as 1A but I found it to be a bit less than that. Approximate FT857 TX current draw:
Some recommendations:
VFO knob - S 4017 ROTARY ENCODER RES20D50-201-1G Q9000709A
e.g. https://www.radioworld.co.uk/yaesu-rotary-encoder-q9000709a-ft-897-main-tuning-encoder
or
https://shop.funk24.net/YAESU-Q9000709A-ROTARY-ENCODER
Selector knob - ROTARY ENCODER EC12E24244A4 Q9000796
https://www.radioworld.co.uk/yaesu-genuine-select-rotatory-encoder-q9000796-spare-part