If you get a part-time job H1B petition approved, you can use it to maintain your status.

With an H1B visa you just need one job (at all times) to maintain legal status. Part-time H1B petitions allows the employer to specify a range of hours, like 10-20.

If you find an employer willing to hire you for 10-20 hours, and file the H1B petition (which costs including attorney fees, around $3k to $4k), then that should free up enough time to do something on the side.

With regard to working on a startup:

In order to legally work for your YC or non-YC startup, you will need another (concurrent) H1B petition approved. This is actually rather hard. Key points:

1) You must own less than 50% of your startup. Someone (usually the board) must be able to fire you. If there is no one that can fire, your startup H1B petition will most likely be rejected.

2) You'll need investment that is sufficiently high that you can give yourself the "prevailing wage" for the region your startup's office will be in.

Use this tool to find out what the prevailing wage for your region is: http://www.flcdatacenter.com/OesWizardStart.aspx

For example, in order to be legally employed on an H1B in the "San Jose-Sunnyvale-Santa Clara, CA" MSA (Metropolitan Statistical Area), you must be getting paid at least $98,342 per year or $47.28 per hour. You'll need to get investment that's high enough to cover that. YC wouldn't cut it. My estimate is that you'd need stable yearly investment (or revenue) in the range of $500k to a million.