Johan is always a good shout as he is relatively cheap at 6 stones and brings a lot to the table. He has a very average WP and DF, both being 5 but does have 8 wounds and hard to kill what helps with durability. He has a respectable Ml of 6 with his relic hammer which has a 3" engagement range and a decent damage track of 3/4/6 with the double positive flips to damage against any models with the Construct or Tyrant characteristic. He also has the option to take 3 Ml APs against the same target with Flurry making him no slouch at offence. He can also just yell off conditions with his Rebel Yell and is an all around solid option for any crew.
Malifaux Child is surprisingly not bad with the Viks as he can copy one of Ashes 1AP cast actions at -3 cast but with a positive flip. Seeing as Sisters in Battle and Sisters in Fury are both 1AP cast actions he can cast either of them helping to free up an AP for Ashes. For 2 stones he's easy to fit in this crew and with being manipulative 15 he's not bad on the defence side either, he also has the ability to heal friendly models but it's not very reliable but is still worth a mention. In my opinion I think he's a strict upgrade from the Student.
Wokou Raiders can be good fun with the Viks. They are Ml 6 minions with a positive flip built in to their attack with a healthy damage track of 2/4/5. They have a range of triggers as well with their Ml but their Coordinated Raid trigger on a mask really shines in a Viks crew. The trigger is after damaging an enemy model another friendly model engaged with the target can take a free 1AP Ml attack. Who doesn't love an out of activation attack with one of the sisters or even Johan? More impotently is their durability in combat, the Wokou Raiders are quite the tar pits in close combat. Enemy models can't cheat against them if targeting their DF and they also have Bulletproof +1. They kind of excel in games of Squatter Rights as they just sit and score VP's all day long and are also quite maneuverable with extra pushes thanks to synergies with scheme markers. Their 0 also makes schemes like Leave Your Mark a breeze.
Those three models all regularly make it in to my Viks lists and all play solid roles but it really does come down to personal preference I feel. I hope this was in anyway helpful dude.