Welcome to the forum.
I am confident that you have nothing to fear. With all respect, I think you will find Tobago almost crime-free compared to Moscow (or most other big cities). This is particularly true in small villages like Castara. Without knowing which guest house you will be staying at, I can’t be specific. However, the owner living on the premises does bring an increased level of security in that thieves are more conscious of being recognised and the owner will be more responsive to unusual behaviour by people hanging about, etc.
Crime in the village has never risen above occasional petty theft or burglary (not that I am trivialising these offences). The hugely frustrating thing is that the main culprits of the small amount of crime committed in the Castara area are well known to everyone. However, either through incompetence or corruption, the main culprits continue to roam free - largely because they dissapear until the visitor leaves the island, making formal identification difficult/impossible. The Twin problem is that villagers do not like to "get involved" and won’t speak to the police. They tend to look the other way. However, I sense that villagers have had enough. I've been involved in extensive correspondence on this matter over recent weeks and strongly believe that the luck of the two brothers considered to be the main culprits is coming to an end and that they will soon be out of the picture for a very long time.
None of the above will not stop me going to Castara next February – so hopefully that helps you to put this all into perspective.
With regard to your second question: the best way to experience Tobago is to hire a car and just drive around the island. I consider it safe to drive anywhere in Tobago – although you must observe our warnings about visiting isolated beaches and other spots. As always, common-sense is critical. If you get lost or drive into a dead-end road in a village, you will find the villagers helpful in 99% of cases, so no worries there. When I am on the island I make a point of driving up roads/lanes I've never been down before just to satisfy my own curiosity and to increase my knowledge and understanding of the island. I regularly find that these roads take me nowhere useful and have to turn round and go back - but I have NEVER experienced a problem while doing so. Curiosity, yes, but normally helpfulness when people realise that I'm lost or might be looking for somewhere/someone. You will find that driving around the island is one of the most interesting parts of your trip - believe me!