The speed limits in Montenegro are 50 km/h (31 mph) in built up areas, 80 km/h (50 mph) outside built up areas, and 100 km/h (60 mph) on motorways.
In Montenegro the motorways are numbered and prefixed with the letter M, the non motorway main roads are numbered and prefixed with the letter P, the smaller roads just have the names of the town that they lead to on the signs.
The Montenegran motorways and the non motorway main roads that I rode on are of a good standard, the condition of the smaller roads are generally good but there is always the odd exception.
Again like those in Serbia, the motorways signs have a Green background with White numbers for the motorway number, the non motorway main road signs have a Blue background with White numbers, and signs for the smaller roads have a Yellow background with Black names.
Petrol at the time of writing was about 1.50 Euros per litre.
I never saw any signs for speed cameras and I never saw any patrolling police vehicles.
Montenegro has lots of great biking roads and like North Macedonia, most of these I found in the inland mountainous areas of the country. The coastal road is very scenic however, it was full of tourist traffic when I was there and it took a long time to cover a few miles.
I did not buy a SIM card for a mobile phone whilst I was in Montenegro so I have no information about how to do this.