Yes, a full service always requires a complete disassembly of the movement. Generally speaking without knowing the details, a movement should have a full service every 5 years. Some movements, like the gen Rolex movements, can last for longer without an overhaul/full service.
Some of the rep watches come with dry movements, some with over-lubricated movements, and some are actually in great shape. Lack of strict quality control is one reason why they cost so much less. Therefore it’s impossible to come up with a rule for when it’s time to service a rep.
Sometimes it’s obvious your watch movement needs a little love: water, your watch stops, it’s not keeping accurate time, or it starts running backwards

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Other times, you’ll be aware of more subtle things like your watch isn’t winding as smoothly as it should. If you pay attention and learn to read a timegrapher, your watch will tell you when it’s time for servicing.
The open source tg timegrapher for your PC is excellent and you can pick up a watch microphone for very little on Aliexpress. The phone timegraphers are not as good but they are convenient and they are better than nothing.