IMHO, a 20th century set is extremely doable of course since you basically find every coin at every show save for maybe an 01s quarter. This is assuming you are only talking about business strikes and no overdates. Of course it would be a cool collection, I simply think you will be overpaying for a lot of relatively common coins because they are "key" to sets that are collected a lot. Just my personal opinion, I would work on classic commemoratives first. Maybe you will discover collecting coins with unique designs is more fun that just another mercury dime.