It really depends on what the map looks like and where the Iron is, if the map is small I would suggest horsemen since a blitz with them can keep the enemy at bay and if cities have some distance swordsmen take to long to get there, but if you've got some good infrastructure then swordsmen would be agood idea. As for mining Iron I would wait till getting into republic or monarchy since Its not really worth the +1 extra shield unless your trying to build a wonder. Depending on where the gems are, I wouldn't use 3 workers to hook them up just yet since making workers early on takes some time, I would rather have them irrigate or making roads inbetween cities, I would go for other lux like wines or ivory but if gems is the only option on the map then hook them up i guess.