Tab is the default key for toggling the mini map. You can set the transparency of the minimap in the settings somewhere, I forget where. It's not a very good map, but it's usable.
Starting point on the passive skill tree and starting stats. That's it, but the starting point on the passive skill tree does have quite a large effect. If you take the starting point of one class but move into another class, you will in effect be a fair few levels behind. You could, for example, choose a marauder and head straight for the mage area of the passive skill forest, but you'd use a fair few passive skill points getting there so in effect you'd be a mage underpowered by maybe a dozen levels, with less intelligence and more strength. There are the intermediate classes, though, so you could start as a templar and head into the mage area only without losing much as a mage. Maybe you could gain enough as a fighter to offset the mage loss, depending on your playing style, equipment and gems.
It's a very flexible system. For example, 1H weapon and shield is generally considered significantly inferior to 2H weapon for a marauder. So someone saw that as a challenge to make a powerful 1H weapon and shield marauder, which they did by taking some skills from the mage area and building an aura-heavy multi-damage type marauder with a huge energy shield. They got to L83 hardcore, which is about as successful as you can get on PoE.