Basically contract labor has been a form of indirect labor adopted by some employers to facilitate the hire and fire of labor according to their business necessities so as to circumvent the provisions of the existing labor laws which are protecting the job security of the employees. Though this practice initially started only with certain intermittent and incidental nature of operations or works which are distinguishable from the core activities of the establishment, side by side, it gradually spread to all activities culminating in the passing of the Contract Labor ( Regulation and Abolition) Act,1970 by the Government of India. As the very title of the Act suggests, its objective is to regulate the working conditions of contract labor wherever it exists and only then to abolish it completely wherever it is possible. But after the advent of L.P.G( Liberalisation, Privatisation and Globalisation) era, the pace of abolition almost came to a grinding halt and engagement of contract labor has become ubiquitous including Government services. Therefore, the answers to yours queries can only be with reference to the regulatory provisions of the Act as given below:
1) Water does not have any definite shape of its own; rather takes the shape of its container. So is contract labor. The contract labor is governed by the provisions of working hours, leave, holidays etc of the laws applicable to the principal employer's establishment. Therefore, whatever the rules relating to national and festival holidays applicable to the P.E's establishment are equally applicable to the contract labor engaged therein. I don't think that any Law relating to national and festival holidays entitles an employee to such a holiday, if he was unauthorisedly absent on the day before.
2) If you go through the relevant Rules of your State, you will find that the licence issued is work-specific only. Therefore, the registers etc., have also to be maintained accordingly.
3) My answer to the previous question applies to this also. It is the work for which the contract labor are to be engaged that requires licensing. If the no. falls below 20, no necessity to take up licence for that work not withstanding the fact the same contractor has some other contract works in the same establishment.