(Trying to decide whether to go minimum cost or midrange on a dust collector for 1-user small shop in particular -- cfpm, filter, what else. My real question, I admit, is whether the Harbor Freight machine with a better filter is a good deal or too tinfoil to be worth considering, but that IS too specific.)
If you ask outright what the minimum specs should be for any type of tool, your question will invite opinion-based answers. It's also possible your question could be closed as too localized since nobody will have the exact same tools and shop configuration as you.
A better question would be, "How do I determine the minimum requirements for a ______ in my shop?"--or, as an example, "How do I determine the minimum requirements for a dust collector in my shop?" This question invites engineering-based solutions which can be adapted to anyone's shop. Although it would be helpful to provide details about your tools and your proposed ductwork/hoses, it is not strictly necessary in order for someone to give you a reasonable answer.
Your specific question about dust collection is related to What advantages does a dust collector have over a shop vac?, so give that a read if you haven't already.
If you provide details about you, your tools and your shop, I think that's a fine question. Example of important information:
- Are you allergic or sensitive to wood dust?
- Do you have a good dust mask and/or air filter?
- How many consecutive hours are you in your shop?
- Is your shop attached to your house?
- How many tools will be running at the same time? (1, I guess from the 1-user shop.)
- In average, how many feet of hose do you need to connect to your tools?
- What is the diameter of your tool dust ports?
- Which tools will you be using with it?
All those questions can influence whether you should go with a better dust collector and/or filter. As others have mentioned in various dust collector questions, we can use Bill Pentz's research to evaluate whether the collector is strong enough. We can also use the average required CFM for your tools to come up with an not-so-opinionated answer.
Since most countries, states or cities don't have laws or requirements on dust collecting for small shops, it will be hard to get a strictly non opinionated answer. Even so, I don't think we should avoid those questions.
In short, yes, it is overly general. The more specific you can be about duty cycle (use level - professional 24 x 7 or weekend hobby, etc.) and expected performance/results of any tool, the better the answers and opinions can be.
My opinion on DC for the hobby woodworker - it is very expensive to buy machines or to modify them with excellent dust collection methods and to buy the DC with enough volume to then utilize the hoods, etc to prevent the very tiny dust particles that can do the most damage to the human body from escaping into the shop. It is far more cost effective and safer to have a DC that catches most of the chips and dust, and wear a respirator to prevent inhalation of the fine particles. In effect the DC is to help keep the shop clean. A good filter should be used to prevent the DC from blowing the small particles it does collect back into the shop. The larger HF DC with a Wynn 35A filter is an excellent choice for following this methodology.