1. 'Not only' at beginning of the sentence requires an inversion of subject and verb. The verb, or auxiliary verb if necessary comes immediately after 'Not only' Not only is he intelligent, but he also.... Not only can he speak 5 languages, but he also... Not only did he win first prize, but he also ... 2. The sequence 'Not only... but also' is a correct, standard and common construction. Learn it and practise it!

1) I believe what is happening here is what is known as a "conditional inversion." In English you can invert the locations of the subject and verb to make a sentence or phrase conditional. It would also be acceptable to say "Unemployment rate would not only be reduced,but the working conditions of employees on very long shifts would be significantly improved." This use of inversion is purely rhetorical in order to help stress the conditional benefits of whatever claim came earlier. 2) It is perfectly acceptable to use "but" and "also" together under certain circumstances. Here, the writer is creating a system of parallelism using the "not only...but also" structure. This is a rather common tool writers use in English in order to emphasize things such as additional benefits without using an overly wordy sentence. Another example of this structure would be : "Not only is Frank kind, but also smart!" This sentence is much more clean than writing "Frank is not just kind. He is also smart!" while providing a nuance of the intelligence being a bonus quality unlike saying "Frank is kind and smart." I feel my explanation may have been a tad confusing, but I hope this helps :)