Honestly....once you start farming NPC's taxes are pretty worthless...so I'd build like 8-9 cottages...you'll have plenty of population for res gathering. Keep in mind in order to build large number of troops at a time you need a large population, since the excess number of workers (The green number to the right of your cities population) is the max pop of the troops you can build. i.e. 2,000 extra pop allows you to que 2,000 warriors since 1 warrior = 1 pop.