alana124,
I use an Oxo battery powered digital kitchen scale to weigh my birds. It's accurate, it has a tare feature so if I have to weigh a bird in a container, I can subtract the weight of the container from the bird- very handy.
You're still 4-8 weeks out from your girls starting their laying, so hang in there. They're probably getting interested in nest boxes right about now, so be sure to have some available. Keep a sharp eye out for eggs where your not expecting tho- sometimes you all but put a neon sign out saying "lay eggs here" and they still lay where ever the heck they want.
Your white tipped cockerel is a different matter all together and there are as many opinions as he has feathers. While any white on a Buckeye is undesirable, I would give you a few things to consider before you jump to cull. White tipped feathers, I've learned from smarter heads than mine, are often feed related especially when birds are young and really going through their juvenile feather sets (come to find out they go through about 7 sets!). Instead of culling based on what might just be a feather fluke I suggest you critically evaluate your fella according to the standard. Pick your boy up and really feel of him. Is he broad all the way through his back? Does his back slope slightly down from the shoulders to the tail like it should? Does he have a nice wide/thick skull? When he's walking away from you, does he have a nice broad spread of the tail? Are his legs well spaced? Are they nice and meaty? Is his keel straight? Does he hold his wing points tucked under the end of his saddle? When you look at him from the side is he more square than rectangle? Does he have a nice neat pea comb with 3 distinct ridges? And of course, what does he weigh? Is it between 6 and 7lbs as it should be for a 5 month old cockerel (leaning toward the 7)? Does he have a slate bar in the under color of his back? Is his coloring even all over with a nice saturated quality?
Taking all of your evaluations in comparison to the standard, how do you think your boy stands up? Do you think he's a good example of the breed? If you think he's a keeper, then keep him!