I agree, depends what kit you in tend to use. 2-wire digital types are freely availabe and easy to fit/connect. With regard to the gate operation, I'm assuming you are automating them? Are you using buried or gate leaf mounted operators? It doesn't matter really as long as you have allowed for leaf size and weight and 'sized' the operators correctly.
As far as using a 'sparky' to do the work, I would recommend you use him to carry out the power feed work and use a security contractor with experience in gate automation to carry out the rest of the install and commission correctly. I am a City and Guilds qualified electrician and if, I hadn't had 13yrs working in the security industry, I wouldn't have felt comfortable dealing with this in it's entirety!
On the flip side, make sure the security contractor has the relevant experience in this field also.
Most automatic gate setups will require a power feed to one side of the gate (I'm assuming you have 2 gate leaves here) to feed the control unit. All other cabling will be in and around the gate itself to connect the operators, safety loops or photcells, and any override switches. The entry system will include a facility to connect an 'opening' pair to the control unit to give the gates the open command.
Personally, I would recommend an audio only entry phone and a seperate CCTV camera to give you an overview of the gate approach area. Video entry phones only give you a very small area for recognition (usually the face) and nothing else. Using a seperate camera will require a dedicated monitor however and this may not suit your needs so I guess you are best place to decide what you personally want from the system.
Hope this helps.
Andy.
