Gusf

Yes it is ought to be just fine. Wax burns off at around 800 degree f so in the range of let’s say 450 degrees to maybe 850 degrees folks often smell the wax. Use a lot of wax, lots of smell. You should not see any signs of carbon as it will burn away in the rest of the firing. Any kiln vent will help this but downdraft vents are often not capable of removing the smell completely …… and they are not really designed to get all the wax smell. So a downdraft will help but not likely to capture all of the wax smell. The smell will however disappear above 800 degrees.
As far as refiring, a simple general way to think of this would be: for a glaze firing, if you have not fired within 300-400 degrees of you finish temperature then you have not done much real heatwork. Silica and alumina don’t melt less than 3000 degrees so they need flux and enough kiln energy  to help them melt earlier. Until your kiln reaches this melting temperature (often called a eutectic) not much is done in the way of useful work on the glaze. So refiring is generally just fine for most. Technically (Per the Orton cone chart) most of the relevant heatwork to maturity is done in the last 200 - 250 degrees of the firing.
For bisque firing, generally it’s not a concern, just rebisque to your proper cone. Generally It’s ok to bisque more than once and often done when multiple layers of decoration are desired.

Make sure you have enough lighting, everything looks good in the dark.    Denice

Show up. Especially when you’re scared, or vulnerable, or avoiding it.

Here is my take:
Yes you can build and super insulate a kiln (compared to typical 3” brick kilns). It is most likely needed for your electrical restriction.  Fiber is certainly king with respect to having to heat a bunch of brick mass each and every firing.
Arduino or equal is fine if you have the time, lots of very nice  temperature controllers out there though for super cheap (20.00 - 50.00 usd) PID, Fuzzy logic, auto tune, and I find their type K interfaces more industrial compared to Arduino. If you are contemplating the arduino then likely  are anticipating solid state relays.  They are very doable and will actually add some capacity to your kiln. They need to be done right though, so use the manufactures cooling data and design conservatively with protection for your SSR.
I personally like using low cost PLC because it’s super easy and proven super reliable by industry but, it’s sort of old technology. Having said that even the most basic have web interface capability, standard k type inputs, data gathering, email engines, etc... without too much custom  effort.
And finally, this is a lot of design work with adaptation of available hardware so getting a used kiln to use as is, or to modify seems to me to be  something I would  seriously contemplate. 
 
Finally - finally, an economical  Raku kiln sounds really doable and fun as a warmup step.
At one time a few folks asked what does it take to design an SSR retrofit for an existing kiln, to which we made a very general video so folks could get a real feel for some of the thought that goes into just that part. You might find it interesting.
 

I would suggest using an economical mechanical switch, dual SSR are an ok idea but theoretically they will have leakage even when good. The definite purpose contactor is an industry established norm and cheap if you take screen shots of the video. Additionally no need for the copper heat sinks, although better you can get larger surface area aluminum for cheap. PM me if and when you decide and I can send you some sources that are very reasonable in price.
Heat sink pic and a PLC teaser of what we build for under 1000.00 at this point.

Hey Ollie. Just completed the build. Turned out better than expected. Only issue is that I did end up using more amps than I previously thought to get it to temperature fast enough. I'll write the specs if ur curious. 
Thanks everyone else for the feedback and great ideas. Rpi controller rocks by the way :). 
@Sorcery holly cow. Glad to see you here dude. Haven't had time for The Nut in quite a while. 
 
The end product: