I am not sure about the limit buy per single number but here is a link from magnum

Magnum website BIG win

Magnum 4D Classic 1st Prize won a total of RM 11, 328, 000!

Kuala Lumpur, October 21, 2013 – Magnum’s Classic 1st Prize number of 5682 was won on Wednesday, October 16 by a group of people consisting of families and friends totaling up to over 100 people. They all got together and spent RM4,000 purchasing the winning number at Batu Pahat, Johor. The RM4,000 purchase consisted of Big Forecast RM 2,672 and Small Forecast RM 1,328.

The female representative of the group came to claim the prize money totaling RM 11,328,000 was accompanied by her husband. The couple has been loyal supporters of Magnum’s 4D Classic game for over 40 years. The winning number was from a car registration number.

The female representative stated that the whole family were ecstatic with the huge win and were overjoyed. She couldn’t stop saying it was such a meaningful winning experience because over 100 family members and friends shared this winning.

According to the winner, “Magnum’s 4D Classic game is not just straight forward and easy to play but the winnings are incredible too! Winning the Classic 1st Prize was a wondrous experience! Never did I expect that the bond we created amongst our family has created such a fortune that will be enjoyed by every one of us. I believe no matter how slim the chances are there is always an opportunity for us to win.” She explained. The female winner has other winning experiences besides from this one and her most recent winning experience was around RM 100,000 at the beginning of this year.

A Magnum representative said, “What a wonderful occasion to have group of over 100 people consisting of families and friends get together, buy a number and win! Magnum’s philosophy has always been to ensure that our customers are satisfied and rewarded for their support and loyalty. What better way to reward them than seeing them happy with their winnings.”