Question - How to choose weight of replacement anti-skating weight?

I have a couple of tonearms that are missing their anti-skating bias weights. One is an Audio Technica AT-1005mk2, the other is an Audio Technica AT-1501mk3.

According to one forum post, the AT1005mk2 came with two weights, one 2.2g the second 1.7g. I guess those were designed to be used singly or both together for extremely heavy cartridge/headshell combinations. If I'm using a headshell weighing in at about 12g, and a DL103 weighing about 8g (20g total), with tracking force of 2.5g, would I want to choose a bias weight of 2.5g? Or do I want a heavier counterweight (e.g., 4g) so I have some room for adjustment/tweaking? Or is the calculation of the weight more complicated than that?

Also, is fishing line acceptable for stringing up the anti-skate bias weight? My AT-1501mk3 came with its weight strung with thin metal string, which I unfortunately snapped. Is the stretchiness of fishing line a liability? Or is that a non-issue?

This is the first time I've tackled this kind of project, so I'm a newbie. Any advice would be much appreciated.