Common indoor plant pests include mealybugs, scale insects, spider mites, fungus gnats, aphids, and occasionally whiteflies. Your description does not match any of those pests. I suspect yours are strays that will not stay and reproduce on your Philodendron so I don't think any treatment is warranted at this point. Of course, you should always remain vigilant for potential pest problems and treat them promptly once they are identified.
There is no exact formula for diluting the alcohol. I know that a 1:5 alcohol to water ratio works effectively on mealybugs and scale and does not require subsequent rinsing as undiluted alcohol does. To be effective, you have to get total coverage of all leaf and stem surfaces with the spray. When thorough, a single treatment is often adequate. Normal spraying will not drench the soil.
