#1
Over the next few months I am planning on building and crafting a guitar by hand. I don't plan on it being the best and I know what I'm getting myself into but I have a few questions.

I would like to build this guitar from scratch, so no kits no pre-made planks for guitar building. But doing this I don't know what measurements to start with. I don't know how long I should cut a neck. Once I get the neck I assume I can use that as a center piece for the body, but I have no idea how long I need to measure out this neck. I'm looking for a 24 fret jumbo neck with a scale length of 24.75" and a head stock that looks like an old kramer (here's a reference image http://www.tommyguitars.com/i/DSC_0356.JPG) I want the radius if the neck to be about a 12"-16". So what size plank should I buy and how do I go about measuring one out, because I know the scale length starts at the nut, and ends at the bridge, but that doesn't give me the measurements for the neck unless I'm thinking about this to hard. 

That's the big question I have with the neck

With the body it's sort of the same issue, I don't want to have a super huge body because I am quite a small guy, my Jackson slattxmg3-6 is a great body size so should I just use that as a template and trace it out? 

Obviously I don't know much about what I'm doing but I want to be a luthier and it's no better time for me to start now. 

Anything will help at all and I appreciate anything you can do to help. Thanks!
#2
A lesson I learned the hard way is to start with an easy guitar. You seemed to hint at wanting to do a neck-thru guitar... I think you should not do that. Just do a bolt on, then a set neck, and then try a neck-thru.

Here are the dimensions I use for a 6-string guitar build.

Body: 14" wide, 18" long, 1 3/4" thick(maybe a little thicker to give you room to flatten and sand if the board is not flat already).
Now this means the total dimensions, including a top. If you want a separate top, then factor that in. For instance, maybe get a body thats only 1 1/2" thick, and then add a 1/4" top to make a total thickness of 1 3/4".

Neck: 4" wide, 28" long, and thickness is 2 inches for a 1-piece gibson style, 1 inch for 1-piece fender style, and 3/4 for a 2-piece scarfed. 
The fender style is the easiest. If you want a fancy headstock, you might need to glue wings onto it to make it wider. I usually make the wings from the neck blank itself after I cut it to rough shape.

Fretboard: 2 1/2" wide, 20" long, more than 1/4" thick. I am never precise on fretboard thickness, but I make sure it is over 1/4", because My goal is to get it to 1/4" once it is radiused. I usually end up getting it a little smaller than that, which is fine though. Just don't start with 1/4" because it will look very thin once radiused. 5/16" is perfect. Dont go more than 3/8" though because then you have to remove a lot to make it the right thickness.

I highly encourage you to watch Crimson Guitars, Wills Easy Guitar, Stewart MacDonald, and other good youtube luthiers to see how they do things. Watch several guitar builds from start to finish to see how the whole process goes. Not just one. They all do it differently and you might see certain things you like from each one.

I started my luthiery journey by buying a band saw, borrowing a table saw, and buying an Ibanez Jem template off of Amazon. I still use that Gem template today to trace out hardware and measurements before cutting. The template will come with everything you need, besides the tools and wood. You can use it to get every dimension you need, but then you can edit the body shape however you want. Since you want that scale length, find a template of a guitar with that scale length instead. 

Good Luck.