It will be very tiring - I came back very tired from each day of my minis. Doing so many in a row will be difficult and to my mind I have heard of no one who has done what you are planning to do. I question why 5 is necessary (especially during one summer). Personally I did 0 in my first summer, and then did 6 spread out accross the whole of my second year (two each holiday).
I am surprised that so many sets offer 2 week minis...I thought one week was the max, and for good reason: I often find that 3/4 days even is enough to learn as much as i need about a set. I agree with TakeTwo's suggestion of cutting them to a week - although I would check out their policy first: perhaps 2 weeks is what the offer is, made on a take it or leave it basis.
I cant say whether or not it will affect your academic performance; this will have to be a matter for your own judgement. Speaking for myself, as i said I didnt do any minis in my first uni summer, but I did go on holiday a lot etc... and didnt do much academic work.