6. What's most important regarding Solar Return interpretation?

Probably the most important thing to look at is the house placement of all the planets. Sign in not generally so important. The Sun is always the same sign. Mercury can only be plus or minus a sign from the Sun. Venus has only eight placements and then begins to repeat itself. The Moon has nineteen placements since it is on the eclipse cycle. Jupiter will be one sign or the other for everyone since it moves one sign per year. Saturn and the other outer planets will generally be the same for everyone. That leaves Mars, which is the only planet that does not appear to have a cycle, so focus on the house placement.