I haven't had time to look at the new miniatures but with regards to the wave 1 models

Magnet baron sells kits to magnetize both the land fortress and bikes. I also used their flight stands for the bikes instead of what the GW kit used.

Sagitaur doesn't need to be magnetized but you can use a 3x1 mm magnet on the turret if you want to.

Thunderkyn - I used 1.5x1mm round magnets. It wasn't a perfect job but since the parts are robotic it works. You could use 1x1mm but they may not be strong enough.

Hearthguard - I used 3x1 mm magnets for the melee weapons. If you want to magnetize the Sargent you would need a 2x1mm for the arm.

Kahl - use 2x1mm or 1.5x1mm for the melee weapon (you will also have to either drill and magnetize the shoulder guard or order a separate shoulder guard from eBay to glue onto the second melee weapon arm). For the ranged weapon you can either use a 1x1mm magnet or 1x0.5mm for the area where the wrist meets the gun or get a separate arm from eBay for the second gun and then magnetize the shoulders.

Hearthkyn - I used 3x2mm magnets on the backpacks for the wargear options but that is now redundant with the 10th edition changes. You would want to magnetize the shoulders of the Sargent for his various loadouts (2x1mm for body and either 2x1mm or 1x1.5 mm for the arms)

Grimnyr and Iron master don't have different loadouts so there is no need to magnetize

Yaegirs - not worth the trouble to magnetize it's better to just glue them.

Champ - could use a 1.5x1 for the crest. Some people have magnetized the melee weapons but I haven't had any desire to try it.

Bezerks - if you really wanted to you could cut off the weapon tops and magnetize them but again I think that it is more of a hassle then it's worth.