The premium account feature, while advised if you wish to perform tasks more easily and often better, is not mandatory. You do not have to purchase a premium account, though some features are more limited or entirely restricted (such as coat of arms, notebook capacity, etc.) without it.
You can play this game without premium acount and do pretty much all the same thing that a person with premium account can do.... they just take longer to do due to the shortcuts ect that premium provides, not to mention that the need to farm efficiently and que buildings while your offline is much better satisfied with premium. As a 300k solo player I couldnt maintain my account without premium and indeed account manager, even though its technically possible.
In conclusion if you enjoy TW and want to progress then the very small cost for premium when weighed against hours of game play.... Makes getting premium as soon as possible (funds permitting) a very god idea.