800 to 900 CCA will be fine and alot better in cold weather.
For the 5.4 liter V8 engine in a 2001 E-350 the owners manual shows that the optional battery is 750 cold cranking amps ( they also show that the 6.8 liter V10 engine has a standard battery that is ( 650 cold cranking amps ) and the optional battery is ( 750 cold cranking amps )
The cold cranking amps that are required to start your Ford 2.5 liter engine is dependent upon the outside temperature. 450 cranking amps are required at a temperature of 32 degrees.
I would recommend 500 minimum.
800 to 900 is plenty even in colder weather.
If you live in a cold climate the more the better.
It requires a group 78 battery. I do not know the physical dimensions of the battery. You will need to get one that has the proper cold cranking amps.
A 12 volt battery with about 600 cold cranking amps works well. A little bigger if you live in a cold climate.
4 cylinder engine / BCI group size ( 96R ) / 500 to 590 cold cranking amps ( CCA ) V6 engine / BCI group size ( 40R ) / 650 cold cranking amps
910 cranking amps 700 cold cranking amps
cranking amps or cold cranking amps Group refers to its physical dimensions.
There is no better, but 800 is more cranking power that 650.
you will need 2 batteries if you are replacing systems needs and they vary between 700 to 1000 cranking amps on different auto parts store web page look ups