Schengen Business "Circulation" visa

Good Day Everyone - this looks like a great site.

I have searched the site to try and obtain specific answers to questions about obtaining a Schengen Business "circulation" visa. However although many threads are useful I would appreciate some advice to my specific situation.

About me: I am a South African who has just arrived in London to work. I have an HSMP visa. I will start work in the next week. The company I work for is a small consultancy that has clients in Europe (especially Germany ) and they require me to undertake regular short (max 2-3 days) trips for face-to-face meetings with clients. (At least once a month)

The Questions:
- I presume that a Schengen Business Visa is required - namely a circulation visa ?
- Which embassy is easiest/cheapest to obtain said visa
- Is it better to initially apply for a 6 month visa (if there is such a thing), and then go for a 1 year - 2 year - 3 year etc.

Other than letter from my company, payslips, letter from company in Europe etc what other hidden "secrets" could I, or the company I work for, "exploit" to obtain this visa as quickly as possible.

Would an immigration lawyer help in obtaining this visa smoothly?

Thanks for any advice/comments if you have taken the time to read this