Many questions, all deserving lengthier answers than I can give right now, but here are a few comments to start; maybe another LawGuru lawyer or two will jump in and provide further details.

First, your failure to answer the complaint within 30 days gives the plaintiff the right to ask the court clerk to enter your default. You don't say whether the plaintiff has done so yet, but if it does, your right to appear in the case and to defend yourself by answering, or by objecting to the attachment at the forthcoming hearing, will be cut off. Once your default is taken, the only thing you can do in the case is file a motion for relief from default.

If you default hasn't been taken, you can still file a responsive pleading (usually, an Answer) even though you're beyond the 30 days. You should do so immediately, if you can. Once your default is taken, as I said, all you can do is move for relief.

Your property as described in the application for a right to attach order will be "attached" as soon as the court acts favorably on the plaintiff's application for the RTAO. That basically means the plaintiff will have a lien on the described property. Sometimes the court will modify the request by excluding certain property. Courts are inclined not to allow attachment of a personal residence, but they can, if that's on the request.

Attachment creates a lien in favor of the plaintiff. The plaintiff still has to win the case and get a judgment before it can attach, levy upon and sell off the property upon which it has obtained a right to attach.

However, if you are in default, the plaintiff is well on its way to judgment and attachment.

Certain property will be exempt from attachment, levy and sale. That's described in the Code of Civil Procedure and the list and rules are too long and complicated to discuss here, but as a general comment, I'd say that the exempted property is not much and you will not be too happy with the result.

An undertaking is a kind of bond that would protect you against damage from having your property subjected to a lien while the trial is pending, in case you ended up winning. The court probably will, and perhaps must, order the plaintiff to post an undertaking as a condition of the RTAO being granted, and probably will give them 10 days to post something like $10,000. (Just a guess, this is kind of typical).