Installing new vinyl squares
It is always advisable to begin your new floor by removing the previous one although not everyone follows this practice.Sheet vinyl, unlike tiles, is more likely to buckle or curl,especially along the edges over time.Again,it's been done but I'd advise removing the sheet vinyl.
Matches is right. However, you can consider installing a layer of Lauan on top first, then your new vinyl. The bad news is it WILL add height to your floor. Doors may not open, transitions into other rooms is going to be higher, and foot space under cabinets (if you have space) is going to be less.
It's just a thought. My best to ya and hope this helps.
Jay J -Moderator
PS: Consider installing some sort of trim around the edges of the room. ANd when you seal your seams, follow the directions !!!
PPS: God Bless America!