The speed limits in Slovakia are 50 km/h (50 mph) in built up areas, 90 km/h (56 mph) outside built up areas, and 130 km/h (86 mph) on motorways
The motorways are numbered. All of the motorways are toll roads. The main non-motorway roads are also just numbered, and the smaller main roads are also just numbered.
The motorways signs have a Blue background, the main road signs have a Green background, signs for the smaller roads are on a Dark Blue background.
The smaller roads are generally in much poorer states of repair than in other European countries, however the other roads are generally good.
I never saw any patrolling police cars and I never saw any speed cameras.
Petrol was generally much cheaper than most countries that use the Euro and at the time of writing was 1.30 Euros per litre.
My favourite Slovakian roads were those in the North of the country in the Tatra mountain region.
I did not buy a SIM card for a mobile phone whilst I was in Slovakia so I have no information about how to do this.