The network topology must by point-to-multipoint and addressed multi-drop to give the possibility to interrogate each electronic device. The communication path, from the main computer to electronic device, must be transparent for the customer application.
I looked at your description and topology and I think you can easily accomplish what you described there with a regular radio (it could be the one you mention) and multiple 485/232 converters. This converters will convert to a single 232 port and even though you have multiple converters (as opposed to the multiple ports you described) you will still have the multi-point to single point architecture.
I can assure you that the FP-100x are not the best option for you in this case and unfortunatelly we at NI do not have a 485/232 converter to offer, but I am sure you can find them in the market for a very low price.