How you configure stitching vias depends on what you want to achieve.
1. If adding vias is itended for increased current capacity then you can use a larger diameter drill and fewer vias. In this case, I would always calculate exactly how many vias I will need to carry current. An easy way to know this is to use pi to calculate circumference of via drill then use this circumference in any trace width calculator to find out how much current each via can carry and how much of a temperature rise I want to allow. (usually within the barrel of a via plating will be about 1 ounce)
2. If adding vias is itended for shielding than I might approach this a bit differently. For shielding, I typically want to use a smaller via diameter but use more of them to create something of a forest effect offsetting each row by 50%. If I am shielding a Tr line I will usually space vias at 1mm along Tr line and 2mm for each row therafter.
Regards,
Eda