I think this is a really fun little indie game, with a lot of replayability and the need to be careful when positioning in dungeons (traps, monsters, and turning corners when both ways are valid) and dungeon fights, and be ready to exit the dungeon when low on mana and mana potions. Your facing when you meet a group of monsters is important, and can make the difference between getting smacked and lightly grazed (there are three scenarios: normal - both sides are facing each other, flanked - one side is facing the other side which is facing left or right and the first side gets some extra turns, and Surprise Attack - when one side is facing the other side which is facing away, first side gets a decent number of free turns before the other side acts).
For an easier and more powerful start, the Defense boosting Wizard is a good one to pick, although all Wizards provide minor (ie. flavor) bonuses. I quite like Morn the Clever for a slightly higher magic item rate. I suggest starting with Tiny maps, then moving up to Small maps. Even Small maps are quite large. It's good to learn the basics in Tiny or Small maps, and even a Tiny map can take multiple days of playing and lots of careful strategizing and RPGing and dungeoneering before you finish it. If you want a few more neutral towns and free resources choose Small, and with Neutral towns that hate another neutral town, if you help one, the other likes you less, so you have to choose which towns you want to add to your empire.
If you want plenty of quests and towns and treasure to pick up around the map, a good size is Normal, but I would try Tiny or Small map size before Normal, and anything bigger than Normal map size will take an extraordinary long time to finish.