The speed limits in Costa Rica are 40 km/h (25 mph) in built up areas, 60 km/h (37 mph) outside built up areas, 80 km/h (50 mph) on dual carriageways and the toll roads.
All of the road signs for the main roads are Green with White writing and the local roads are White with Black writing.
The main Costa Rican roads are Highway 2 and 34 in the South of the country below the capital San Jose. In the North of the country the main roads are Highway 1 and 35 that both lead to the border with Nicaragua. These are generally in good condition. The condition of the smaller roads is generally good and they appear to be well maintained. There are no motorways in Costa Rica but around San Jose there a couple of toll roads. The English version of the website explaining the toll roads and their costs can be found here.
https://globalviaruta27.com/inicio-english/
I would not recommend riding in any foreign country at night however having been forced to do so on my first night in the country, I found it to be reasonably safe with the exception of cyclists using their bicycles on the roads at night without lights.
Petrol at the time of writing was about 1.45 US Dollars per litre.
Costa Rica has a very small police presence on the road and I never saw a police speed trap or a patrolling police car looking for speeding vehicles.
To buy a SIM card for a mobile phone you need to go to any large general purpose shop or supermarket where you can buy one without providing ID. To use the SIM card after purchase you need to find a shop that sells a top up or that will top it up for you. When I did this the cost was around 5 US Dollars for the SIM card and a further 10 US Dollars for 14 days of internet, although I did not get to find out how much data I had purchased.
When entering Costa Rica you are required to purchase mandatory vehicle insurance and when I did this it cost me 45 US Dollars for 3 months of cover. You also have to prove that you have appropriate insurance before you can apply for a Temporary Import Permit (TIP) allowing you to legally ride your bike in the country.
I bought the mandatory insurance and the TIP was issued to me for free. When applying for the TIP you have to fill out a form in where you record your passport and vehicle details, you also have to specify what length of time you want the TIP to be valid for, I opted for 14 days. I left Costa Rica before the 14 day TIP had expired. I was told at the border that I did not need to cancel the TIP but I could suspend it until I returned which I chose to do.