First question would be whats the risk, theft attractive stock or property, area, etc etc.
Second question value of contents if you were burgled how much would it cost to start again.
Third question what does you insurer want? Read the small print
Fourth would be site history have you been burgled before.
Lastly what sort of physical security.
This would give enough info to advise what you need.
However, the difference between professional installers and diy is miles apart. Its a bit like going to a barber and cutting your own hair, If you dont want to look like Arthur Scargill then its best to go to the barbers. Professional installers will do a much better job, its unlikely to activate falsely, and more importantly it will work if you have a burglary. CCTV wise There are a lot of very good DIY systems out there but it is a bloody minefield, a pro should know the latest systems and design the system to your requirements. If you have no idea what BLC or HLC stands for then its better to get a pro in. Dahua and Hik are the main two Chinese brands and cant be beaten by anything none Chinese.