Here’s your starting location:
Put Julian at space 14 so he can recruit Ricardo at the first turn. Ricardo is located where the cursor is in the next picture:
For your initial moves, Doga should start at spots 10 or 12 so he can cover the bridge in your second turn. Your strong units should be in a line formation so they cover each other sides, preventing multiple units from attacking them, and weak durability units behind.
After you kill the initial mages and social knights, split your group in two. One group will head to the north, it should be Marth, Sirius, a bow user (preferably Kashim, he has more movement and actual attack speed) and the pegasus sisters. Give them some vulneraries. Your priority is to kill the thief. Make sure that as you move, they don’t get near the snipers, or they’ll attack you. After that, when you are near the village, lure the dragon knights slowly and kill them with arrows or silver lances.
The rest of your team should head towards the castle. Due to the bridges, you’ll be fighting enemies one by one, so there will be no problem to kill with an unit in the frontline and someone attacking from behind. After the social knights and the armor knight are dead, kill the ballistas with the units that need experience the most, as they are a joke. Same with the thief reinforcements.
After that, while you move Marth to seize, buy a live staff or two and whatever weapons you need.