This kind of stuff has been posted on here so many times before, please search the forum for discus and read everything you can find. Also use Google for more info, spend time researching and decide if discus are right for you. Some thoughts:
1. Do you know about cycling? I was surprised about your comment of emptying your tank and saying in a week it will be ready for discus. If you don't have access to matured filters or a way to keep them mature then you will need to recycle the tank again. Discus should not be added to newly cycled tanks!
2. You'll need to match the water parameters of your supplier for best success. Research ph, and hardness, and the use of RO water. Ph 7 or under and soft water are required IMO, though will find people selling and keeping discus kept in hard water they just don't seem to do so well.
3. Find a decent supplier to buy your discus from. As your a newbie I would suggest fish around 4" are best ( less chance of stunting them, and they will settle in better). Be prepared to spend around £50 per fish for a nice one, though prices do vary slightly.
4. You'll need to keep them at or near 30C, make sure your heater can cope with this.
5. Be prepared for the water changes and maintenance. Running your own RO filter can sometimes be a pain and it's easy to skip water changes. Be prepared for 2 - 3 a week min, more so in your size tank with plecos I would suggest.
6. You can't sex discus, until you see them breeding.
7. If your LFS has told you they have 'mini' discus they are either ignorant or lieing, either way find another supplier!