I am planning to go from the UK to the Slovakia on the 3rd of August in the evening or so. Is anybody planing similar route this time?

well, I'm planning to go to Slovakia on 31.July - 1.August. My route: Latvia - Poland - SLovakia - Check Republic - Poland - Latvia.

Can someone advice on "must ride" routes in Slovakia?

Have a look on this map. But there is much more routes you can ride.
https://maps.google.com/maps?saddr=R...,4,7,8&t=m&z=8

When you enter Slovakia be careful. Car drivers are arrogant, there is lots of police patrols on the roads checking speed 90kmh on carriageway 130kmh on motorway. On the motorway usually black Audi or Passat. You must carry spare bulbs, first aid kit, warning triangle, high viz., bike owner certificate, insurance certificate. On the route (google one) there is several camp sites you can stay overnight. Or you can find B&B in small villages for about 10-15 Euro maybe less. If you have more questions feel free to ask.

thanks for tips

are you sure about warning triangle and spare bulbs?

I've found that warning triangle is mandatory for vehicles with more than 2 wheels.