if you consider new zealand's climate and also your type of car and milage, i would say 10 30w would do the job just fine(thats what i run in mine). as for brand, you could pick up a 5l oil and filter from subaru from around $90 which is probably your best option, or you could get some aftermarket oil from repco, such as Valvoline, nulon or castrol edge etc..
usually subaru's are serviced every 10,000 ks but it depends on many conditions. some people tend to change the oil at around the 5000k mark.