How should I go about bringing up a prototype crystal oscillator? (+ load capacitor question)
The effective load is 82pF in series with 20pF or about 16pF, plus stray capacitance, so maybe 18 or 20pF.
That amount of difference will probably cause 20 or 30ppm additional error in your crystal frequency.
It sounds like you've done some reading about it already. You can try lower value capacitors, test at temperature extremes with resistors that are significantly higher/lower than your design values, calculate worst-case dissipation from ESR and so on. Since you don't have the equipment to actually confirm margin on the 1uW maximum crystal dissipation.
If you really need reliability then you might think about just purchasing a packaged 32.768kHz oscillator for about $1. in singles.