Totally agree with the recommendation to go for the Microchip one. The one important thing to keep in mind about the RN2903 is that it is not very easy to solder, so try to get a bunch of them in case you burn the first ones.
About gateways, I wouldn't really bother much with the single-channel gateway; it is good for some testing, but it won't give you any meaningful way to kick start a community. I would recommend the LinkLabs board that @jpmeijers linked above or the IMST one (the latter is the one we're using, check here: https://github.com/ttn-zh/ic880a-gateway/wiki).
Saludos