What is the best patent strategy for early-stage startups

You can certainly start by filing one or more provisional applications. If your disclosures are truly decent, meaning, they truly disclose what your invention is and how it works, you can file it as a provisional application relatively cheaply - the filing fee for a small entity is $130.00. However, if your disclosure is not in good shape re really disclosing the invention, you will need to work on it because you will eventually have to file a non-provisional application in view of the fact that a provisional application never gets examined and never leads to a patent in and of itself - but if the provisional disclosure is not effectively complete and thorough, when you file your full-blown non-provisional application, if critical parts of the invention were not disclosed within the provisional application, your non-provisional application will not be accorded the priority filing date of your provisional application. If your technology is important, it is best to invest in having a good provisional application written.
Also, it depends where you are in the development stage - if your invention is complete, then you can file either a provisional or non-provisional application application - again, if your disclosure is good, you can probably get away with a provisional application and then use that disclosure to attract interest and funding. Or you can proceed directly toward a non-provisional. If your invention is at the prototype stage, you may want to file one or more provisional applications for the various improvements developed over time, then file a non-provisional application within one year from the filing date of your earliest provisional application. If you want to obtain foreign patents, you will need to, for example, file a PCT application also within the one year time frame from the filing date of the first provisional application.