SLC 5/01 upgrade

I'm thinking of upgrading our SLC500/01 PLCs to SLC5/03 or SLC5/04, because I need more than DH-485. My questions are :
1) Will SLC5/03 module fit in SLC5/01 chasis?
2) Will SLC5/03 module work with my existing modules, such as 1746-IA16 and 1746-OW16 and 1746-IG5 (5volt DC)?
Any response will be appreciated. thanks.

thaque

Simple answers: Yes, and yes

The new processor will indeed work with the chassis and modules. The chassis and modules do not belong to the processor, they belong to the same family as all the SLC processors, meaning all processors, modules will play well with each other.
You may notice nuisances with an old program or old version of RSLogix in the new processor, but these should be easily corrected.

Is it safe to assume that by wanting more the DH-485, that you want DH+? If so you will have to go with a 5/04 to get the connectivity you need.