Thanks for the advice ^ I have now contacted the embassy regarding the additional equipment via email, just waiting for a reply.

Thankfully as a UK citizen I won't need a Visa for non-remunerated activities, the Mexican Embassy website stated the following:

Business Visitor Carnet VISA: According to Mexican Immigration Law which came into force on 9 November 2012, British and EU nationals who are going to undertake the following “Activities Non Remunerated” in Mexico for less than six months are exempt of Visa: the beginning or execution of an investment project, to give technical or professional advice to public or private institutions, business meetings, lectures, courses or training of staff, to perform an audit, repair or install machinery and software, to design or start the operation of a plant agreed previously on contracts, or to give services agreed on transfer’s contracts of technology, patents or marks. Simply they must fill in a FMM migration form (landing card) obtained on the airplane or at the port of entry in Mexico and declare the purpose of their visit.