Deposit is due Thursday. I still don't know how the bid-down rounds work.

Your $12,000 across six certificates at $2,000 each is fine on paper, but check the per-certificate fees before you decide on size. My county charges a flat recording and issuance fee per certificate. On a $1,200 lien that fee is a real chunk of the first year's interest, and if it redeems in month two you're basically working for free. Six small ones costs you six of those fees. Two bigger ones costs you two.

Separately, where did the 2% to 9% spread come from? If the 2% ones were the houses, that's the whole game right there and your budget isn't going to buy any of them.

Look at what the assessed value is actually attached to. I've been pulling parcel cards on these for a few months and the ones with the low tax bills are usually land with no structure, sometimes strips that were left over when a subdivision got platted. Assessed value of $9,000 on paper, worth nothing to anybody, and the owner stopped paying because they forgot they owned it.

That isn't automatically bad if you only care about the interest and the redemption comes through. It's very bad if you're secretly hoping you end up with the parcel. Which one are you doing? You didn't say, and the answer changes which of the 340 you should even be looking at.

Asking the thing I would have been embarrassed to ask: what happens if you win more than your deposit covers and you can't fund it? Some platforms will just cancel the award and keep part of the deposit, some bar you from the next sale. I'd want that answer in writing before I wired anything, because it's the difference between the deposit being a formality and it being the actual constraint on your plan.

Also @anchor, two days is plenty for this specific decision. It isn't plenty for picking six parcels you've never seen.

Deposit rules are set county by county and the two things you read both exist in practice. Some jurisdictions treat the deposit as a hard cap on total awards, some treat it as a percentage of intended bidding with the balance due on a settlement date after the sale. That's not something you can reason out from the general mechanism, and a form email doesn't resolve it. Call the treasurer or tax collector and ask them to point you to the paragraph in the bidding rules, then keep the reply.

On sizing, the arithmetic @bramble raised is the one that governs. Interest on a redeemed certificate accrues at the statutory rate from a date fixed by state law, and in most bid-down states you are bidding that rate downward, so a competitive parcel can clear at a rate that barely covers your fixed costs. Some states set a minimum return or a penalty floor that applies regardless of how early the redemption comes, and some do not. Confirm which applies in your state before you assume a two-month redemption is profitable.

The deeper issue is that your plan has no stated purpose. Fixed-income lending and property acquisition are different bidding strategies with different target parcels, and most certificates redeem, so acquisition is uncommon rather than a plan you can rely on. If you're bidding for yield, the low-rate improved parcels are where the competition is and you should expect to lose most of them. If you're bidding hoping for a deed, you're buying procedure and years of waiting, and the parcel needs to be worth that on its own.

Decide that first. The deposit number follows from it.