Spanish to English Marketing Marketing

It seems I am having to ask quite a few questions with this text, thank for all the help! My problem here is that the author seemingly has put in a phrase that has no connection to the rest of the sentence. I mean, is it just me or is that little phrase just totally unrelated to the rest? I realise this is not your normal question, I am hoping someone has a good work around or an answer as to what the author is getting at.
I have posted my rough draft translation below. Cheers!

Orig:
Se han estudiado los costes obligatorios y también aquellos voluntarios derivados de la iniciativa propia de los establecimientos de implantar determinados sistemas o certificaciones, generalmente, para satisfacer exigencias del mercado en que trabajan los hoteles, que, clasificados por tamaño, soportan adicionalmente a los gastos propios de su actividad

My rough draft:
In phase one we also studied compulsory costs and costs related to the voluntary acquisition of certain certifications or systems, generally done to satisfy the demands of the market in which the hotels operate, which, classified by size, must also pay costs related to the operation of their own businesses.