Jeff, I like your mind set no sense doing it unless you do it right the first time, which I didn't on my first furnace and a couple of other that I build, but I'm no furnace builder. I do know a couple things that will work that you may want to look at incorporating into your furnace.
you can tell me to be quite if you want,
Number one, is use quality materials, if you can get em cheap enough use the white alumina oxide brick to build your furnace with the 2600 degree ones, it makes for a simple build cut with an old handsaw and place em in the furnace, don't worry about mortar use a shell that you can tighten up with bands and your set for every thing up to cast iron.
number two, you burner there are a lot of good designs out there, you just have to figure out which one is going to be your workhorse burner, if you want to try others find but don't mess with the one you have that works. What you want to burn for fuel and how cheap you want to do it, is something you will have to decide. lot of people are using oil some will tell you that waste oil is hotter. I'll tell you that it can cause problems with plugged nozzles and things like having to heat it or thin it with diesel or kerosene. A lot still use propane. Myself I have sorta switched to a dual fuel burner I guess you could call it, I ca burn oil and propane at the same time or just one at a time, and believe me when it tell you the thing gets hot, even on just propane at 4 to 5 psi its HOT.
number three, drain hole like harry says put it in the side if you don't need it plug it with some ceramic fiber, you make you furnace right you can as Harry says scrap in it. or melt items to large to get into a crucible, and let it run out the side into an ingot mold or throw em in a brush pile and set it one fire pick up the melted stuff after it cools.
Wood splitter works great for busting up car wheels tranny cases, water pumps,
Sources for material to feed your new hobby are any piece of aluminum or brass or bronze of cast iron that has BEEN Casted before. Screen Doors and Window frames don't make the best casting material. unless you got some good stuff to mix it with, or you allow for a huge amount of shrinkage.
get yourself some reference material's Principals of Metal Casting put out by the AFS American Foundrymens Society is a great book and everyone should have it. cost about 15.00 from ABEBooks.com
Crucibles, buy em, they just work better then a piece of pipe. they are made to melt metal in, pipe is made to pump water thru. Take care of em on aluminum they will last a long time. on cast iron I won't use anything by Silicon Carbide. Clay Graphite for any thing else.
Fluxes, as for as I'm concerned, buy them also, salt is for the dinner table, the commeercial fluxes that are out there don't cost that much and do a much better job. i used some yesterday on a pot of aluminum that was almost totally clear of anything floating on top of the melt, when I put the degaser in it, what came out of the melt was almost a cup of oxides floated up. Salt won't do it and there are people that will tell you that you don't need to use it, you want top quality castings you gotta use the good stuff.
Yea I get long winded at times, but don't do like I did when I build my first furnace and had the lid hinge up instead of swing to the side. Bad mistake having that lid flipped up looking you in the face while your trying to pull a pot of hot metal out of the thing.
David Happy Holidays enjoy your new hobby,
two of my casting projects, the flask is on going in that I am starting on my third revision of it, this was the first. the two handles you see laying on it were attempts at replacing the handle on my recliner that the square hole stripped out in. dang wood screw the furniture make put in broke.
you will want one of these also/