Re: How do I & Should I - file a lis pendis?
"Lis Pendens" is the old "legal Latin" term; it's now officially known in California as a "Notice of Pendency of Action" (see Code of Civil Procedure sections 405 and following) but everyone still uses "lis pendens."
The purpose of a lis pendens is, as you suggest, to notify everyone that a lawsuit that may affect title to, or possession of, real property has been filed.
CCP section 405.21 requires that a plaintiff not represented by an attorney must obtain prior permission from a judge before filing and recording a lis pendens. This requirement is imposed to prevent their improper use, e.g. to disrupt a deal or out of spite or malice.
If there is a plaintiff's attorney "of record" in the pending litigation, the attoney may sign, file and record the lis pendens without a judge's prior OK, but the attorney faces discipline if the lis pendens is improper.
There may be a question here as to whether you have sufficient grounds to file a pre-emptive lawsuit. If the seller is now actually in breach of the purchase contract, as it seems, you probably have a legitimate claim to take to court.
The possible cost of any real-property litigation goes well beyound the preparation and filing of a complaint and lis pendens, of course. There's a summons to serve, then the other side may mount a strong defense, including despositions and other discovery. Before you decide to file suit, consider whether the seller has any real defenses. If not, you'll probably get a quick settlement and your deal will go through.
A final thought is whether your purchase contract has an arbitration clause. If so, that may impact your right to file and maintain a lawsuit. I do not know whether this would also make filing a lis pendens improper; that's an issue I would have to research.