I think I've found a solution to my first question, this tool offers exactly what I'm looking for:
Merge Excel worksheets by matching data in munutes
"You can update only empty cells in your Master table. Check this option if you don't want to overwrite existing values in your main table."
Does Easy-XL support this? Because really all I wanted to do is to keep the data in Sheet 1 but add new data from Sheet 2 that is not found in Sheet 1.