RFIs should fall under FAR 5.205(c), Special notices: Contracting officers may transmit to the GPE special notices of procurement matters such as business fairs, long-range procurement estimates, prebid or preproposal conferences, meetings, and the availability of draft solicitations or draft specifications for review. This category of special notices does not have a required response time. The required response times in FAR part 5 are applicable to contract actions such as presolicitation notices, how long solicitations have to be posted and applicable modifications. 

When possible, site visits help industry better understand government requirements and are considered a way to promote early exchanges of information. Normally, the government doesn't ask for a site visit in RFIs. The RFI can provide information on a planned site visit.