It is better to use EtOH as the recrystalization solvent. It disolves the salt better then IPA. Crystals from IPA tend to be too fine, and tend to come out too quickly trapping impurities and producing poor crystals. It is better to gas IPA to a reasonable concentration (must dry gas *before* bubling the IPA) and I also think it is better to allow the IPA/salt solution to slowly come to room temperature, then slowly chill, then filter, not evaporate the IPA. The remaining IPA contains a relatively trivial amount of salt but it can be recovered with little effort albeit slowly by just dumping it into a bucket and leaving it unattended where it can get a couple of weeks of sunlight, or a larger dark colored open vessel placed in direct sunlight (ie large animal water troughs).
This can be done at a very large scale. It's possible to adapt a large plastic tank (pesticide, wine, etc.) and heat it with the wires from heating pads to over 60' by enclosing the tank and wires carefully with non-flamable insulation. The tank can be easily and thorougly mixed with one or two impeller driven pond pumps. Hundreds of litres sized reactions are possible and fairly straightforward. Agricultural purposed tanks come in all sorts of configurations. You can buy tapered tanks in 100+ gallon sizes that look like large sep funnels. With those sorts of tanks it's possible to set up the output of the crystalization tank run through an in-place filter to a solvent recovery station, you just have to pressurize the main tank (the presurized air should be well filtered for compressor oil).
Yellow gunk sounds like the un-rearanged freebase. It seems to glob up in solvent. It has a charecteristic smell. Freebase doesn't really smell except for the fine particles that seem to premeate everything, including nostrils. Never seen any commercially produced freebase of such low purity that that happened but you should consider saving it for further experimentation.
