What should I consider with new electrical lines in an old house?
The answer to your first question is YES. You need to have the junction in a box. Can you mount the box higher on the roof or a rafter or a gable end stud? if you don't have enough wire, then practically speaking, the box will have to live under the insulation. Technically it is not enclosed as in being sheetrocked over, so it is not a code violation in an older house.  but when you do bring out the new wire, be sure it appears above the insulation before you go back down into a wall. you could also tag the wire with a label.

The answer to question two is very simple. You do not need to run NM cable (Romex) in a conduit in a residential framed wall. You also do not need to secure fished wire except in the actual devise box entry hole.