Although you may stay in Dawnport up to level 20, I strongly recommend to go to main ASAP.
If your sole purpose is to train ML in a safe environment while making profit, clearly MAIN is your to-go place.
You can activate the Daily bonus and recover twice as much mana, soul and stamina inside some protection zones.
You can readly sell the items on the market.
You can stash more than 1k gold.
You're not constrained by your capacity.
You can train offline and get even more Magic Level while not being online.
There is, literally, no reason to stay in Dawnport, there may be some benefit of staying in Rookgaard though.
Bear in mind that some 'things' can't go through the boat from Dawnport to Main.
Please, before attempting such a feat, read further on the restrictions of 'things' while on the boat to Main.