We plan to deploy NSX DFW as second Tier firewall on the network.
We are not going to use any routing/switching technology of NSX, should I change the Distribution switch MTU to 1700 for this case?
When you still use NSX-T only for the DFW it is still not necessary to change the MTU to 1700. But anyway it is recommended for a long-term plan. Maybe if an overlay will later implemented.
Enabling jumbo frames aka setting MTU higher than 1500 on VDS is kind of an indication that jumbos are also supported in physical infrastructure as well. If it is not set there, I wouldn't change it on VDS either.
When you're choosing overlays, then you should check that all paths between TEPs in a same TZ are jumbo enabled concerning every on all intermediate switches and routers while in your control.