It is an Agency they pay weekly, you have to work a week in hand so don't receive pay the first week you get paid the second week as all agencies, this question is Irelevant
Weekly wouldn't recommend
Whether your pay is weekly or monthly depends on your role and your contract. Try getting in touch with your local branch and speaking to a consultant there to help you find your ideal role. Then you can enquire about pay dates in relation to the role you're applying for.