Will this work?

I'm trying to insert data for a real-time application that demands less than 3 second receipt-to-commit time, has a relatively large (500,000 records/hr) data rate, and requires access times on the order of 10-15 seconds. We're storing about 24 hours worth of data on a rolling basis, so I've partitioned the table by hour. Three of the columns are (separately) indexed.

I know I can do this by piping data through sqlldr into the live table as long as partitions are small enough to keep the index modifications from becoming too taxing. However, I'd like to keep my hardware requirements to a minimum, since I have about 100 of these streams in all, and would like to avoid spending $10M on hardware to brute-force this. So I cooked up a scheme I thought would save on hardware.

I know if I can direct load data into an offline staging table it's considerably more efficient, but in that case I won't be able to satisfy my 3 second receipt-to-commit requirement unless my partitions are impractically small.

I plan to have a partitioned, unindexed table to receive data the
"loading" table). Once I get enough data for a full hour, I'll
exchange the partition with an unpartitioned table's data segment (the
"staging" table). Then I'll build the indexes I need for the
destination ("live") table, and exchange the newly indexed table into a partition in the "live" table.

The idea here is I can do indexed searches on 23 hours worth of data, while being able to direct-load my source data without recalculating indexes. The reason this will work for me is actual _access_ to this data is relatively uncommon, so I think I would rather deal with a full table scan on the "loading" table every once in awhile than take the performance hit from updating indexes every second.

I plan to create a view to access all three tables at once. I have a couple of questions, though:

1. Can you access a table while you're building indexes? It seems like I should be able to do non-indexed searches of tables while they're being indexed. Is that true?
2. If I'm selecting from a table, does the select block the partition exchange? If it doesn't, is the result set determinate?
3. What I really want to know, with all this table indexing and data segemnt swapping, is what are the chances some of my data is going to fall through the cracks?