The more I think about it, because yours is an educational installation (rather than your own personal system or even your own personal place of business), you will be better off having a professional (probably a small mechanical contractor) do the design and installation. While there is the potential liability issue, I would think more about the future: future users, expansion, maintenance,
etc. There may be administrative issues – institutional requirements for bidding, capital improvements, budgets, etc. - that may affect limit you doing the actual work.
But there is a large labor cost to this. The materials are relatively inexpensive, but the labor will be significant.
Per your original post:
For an off-the-shelf compressor, manufacturers size the tank (aka receiver) based on the compressor output and the motor (such that the motor won’t start – stop – restart in too short of a period of time). There is also the underlying assumption that the total air demand of the purchaser is less than or equal to the compressor output. For a small application, with only one or two tools operating at one time, the tank sizing is not that rigorous. The tool operates at a constant pressure, assuming that there is a dedicated regulator near the tool inlet. The pressure in the receiver operates over a narrow range; a pressure switch activates (and deactivates) the compressor. The compressor output (in cfm) should be greater than or equal to the usage rate required by the tool. Though you could operate a tool with a higher demand than the compressor output for a short period of time until the receiver pressure gets too low (but that may affect tool performance).
Note that motor horsepower is incidental to the compressor selection. The compressor selection is based on the demand of the tool(s) and the pressure required by the tools (plus additional pressure for the pressure switch controls). The compressor’s pressure output and flow rate (plus efficiency of the compressor) will then determine the motor horsepower.
With more than one tool being used, there is a trade-off between compressor size and receiver size (though I suspect that this becomes less important with smaller
compressors and small users simply because the equipment options are limited). Technically (for a large shop), one would go through the exercise of estimating the demand of each tool (looking in the owner’s manual) and the time and frequency of operation of each tool, and what tools are operating at the same time. A large compressor with an output equal to the demand of all of the tools at once with a nominally sized receiver (that is, large enough to minimize motor starts) is one choice. An alternative would be a smaller compressor to match the most frequently used tools, but with a larger receiver sized to accumulate and discharge enough air for other tools used for short periods.
But such an analysis for a small system will be overkill. Most likely the two or three tools that would be used at one time will equal the output of one of the smaller off-the-shelf compressors that include a minimally sized receiver that “matches” the compressor and motor. (Future demand and/or wish-list demand also needs to be considered in the compressor sizing.)
[After I drafted this I realized I was reiterating a lot of what Footer and Van said…]
Joe