I used to do some calculation to determine an efficient amount of posts needed to earn pc on a daily basis and to reach 8300 play coins in a year (365 days) it's at least 23 play coins per day, roughly translating to about 10 quality posts in the forums daily (depends on which forums you post in, some give 2 pc, some 3pc). A year isn't that bad for compromise, given you earn more pc daily.
But that's only relevant if you're willing to commit some time of your day for quality posting. I did at one point have 8k play coins where a good chunk of it was from posting. Also note that posts should be within site rules
And of course, you can get some play coins by contests, services, or selling stuff.