LVM expansion and new volume distribution

I'm looking at SSD's. I have two SATA III ports. Right now buying two SATA III SSD's is too much money for me. I want to eventually run two SSD's in RAID 0 for my OS. I have also read that newer kernels support TRIM in LVM, so LVM would be the ideal way to RAID the OS on SSD's vs mdraid.

Now if I get just one SSD and install the OS on an LVM volume (Fedora seems to create two volumes by default even when only one drive is involved and makes it look like one drive) how will the data be distributed on the second SSD later on? Now given the Fedora example there are two volumes that I'm guessing will be written to in a RAID 0 stripe style. When lets say two more volumes are added on the new drive will the bulk of my writes still be on the first drive or will LVM stripe them across all four volumes? Or to even things out, can I move the second volume, before adding the two new ones, to the new drive, then add one volume on each drive? Then again maybe it won't RAID 0 them by default since that would kill performance on a single standard HDD. So would I setup RAID 0 only when the second drive is added and still how would I get all the data evenly striped across both drives after writing the bulk of the data to the first drive?

I have experience with a proprietary volume manager at work, but I have zero experience with Linux LVM, so I may have misconceptions to how the data is manipulated.

Wouldn't you generally first make the raid with the disks (mdraid) and then use LVM with the raid device (ie md0) as a physical device allowing flexibility with partitioning etc?

Well yes but two issues. I'm trying to see if it makes sense to buy only one SSD now and just be able to rearrange the volumes later when I buy the second one. And using mdraid for RAID 0 will make it so I can't use TRIM on the drives. A recent update lets the TRIM command be passed through LVM volumes.

Maybe pick some drives where trim does not make such a big difference, like Sandforce? Not so good options, but I don't think you'll have a lot of good options in a gradual move to raid 0, isn't the whole point to stripe your data over two drives, that's not going to be so easy once it's evenly on the other one...

I might be wrong any way, I was never a big fan of raid 0.