$450 for a conversion is a lot of money. If you can afford it then skip the following.
Wheels you can keep, just get a cog from an old cassette or a cheap Shimano BMX cog. PVC pipe works in theory, but getting it cut straight enough can be a PITA.
For cranks/BB, get a cheap Sugino crankset, square taper. Not only is a setup like that real cheap but it also makes a great singlespeed setup. BB will last forever and is dirt cheap.
A half-link should allow you to run a magic gear. The true singlespeed experience can not be had with a chain tensioner IMO.
I was lucky enough on my SS build to get the gearing right on the first try where I didn't need a chain tensioner, but I use one anyway. I noticed once the chain starts to wear a little bit it needs to be tensioned with a tensioner or replaced to get the chain tension back to where it was since I don't have horizontal drops or EBB. I agree it would look much better without it, but I love this frame too much to part with it and my set up works with no issues. If you do decide to run a chain tensioner I highly recommend the Rennen or DMR. I've used the Rennen for the past 6 months with zero problems. The DMR is the same exact design, but made of stainless steel instead of aluminum and much cheaper.
I would also recommend SS specific chain ring (blackspire, salsa, etc) and chain (SRAM PC1 - about $8). I know it's not neccessary, but it will last longer.
a certain amount of chain slack isn't a big deal. running the magic gear, you basically want it to barely fit with a new chain, so that it's a little loose by the time you need to change it.
contrary to logic and the rules of grammar/pronunciation for the english language, it actually is spelled 'family'....