Should be pretty okay in softcore.
I've done it in HC with as a 2h ranger before.
Do keep in mind though that melee is always tougher than ranged in the game. So provided you don't mind that steeper curve and can afford the gear costs, melee Ranger is pretty decent & fun.
Not sure. Fire is tricky. Depends what you are doing with fire; totems, hard casting, 1h/shield, staff, fire traps, etc.
Fire just gives raw damage. Not the most damage, which is lightning. That means you have to plan around the limitations of fire. Since it doesn't provide the burst of lightning or the safety of cold.
Might want to combine your fire build with another element [such as lightning] or minions. Depends on what kind of and how you are casting those fire spells.
Rule of thumb for CI that I find works is; if you have about 3 times as much ES as life, CI is safe to take.
Also if going for Armor/ES gear you will need to find strength to equip it. Note that Armor/ES because it is hybrid gear has less ES than pure Int gear. Which may not work as well with the new CI.