How to handle multiple inflight transactions from same address? How are multiple inflight transactions from the same address handled? From my understanding, there are two options depending on how change is handled, but both seem to have substantial drawbacks:


If change for each transaction generates a new address for the change - the usual handling - then you can't handle two transactions since they will both want to use the same unspent output address. And they will both use it entirely by definition. The ergonomics of this seems poor - I can only ever do one transaction from an address at a time. In that case I would want bitcoins sent to me to always be shredded (no bills larger than $20 please).
If I have change sent sent back to the original address, does it matter in what order they are added to the chain? I can't see why. This however allows everybody to track my wallet and where I'm transacting. Also I don't know if all wallets support this.


Is my understanding correct? (This all started with me diving down the rabbit hole on how Lightening and Plasma worked.)
Addresses are a construct of wallets. The bitcoin system itself doesn't know or care about them.  Coins being spent are identified by their creating txid and output-index.  

The network verifies that the provided signature is accepted by the required scriptPubKey, but the scriptPubKey (nor the addresses that wallets map to scriptPubKeys) is never used to lookup or in any way reference the coins being spent.

The model you seem to be imagining is more like some other altcoins and can indeed have poor ergonomics.

Normally change goes to a new address and those coins can be immediately spent without waiting for the first transaction to confirm.  It sounds like from your question that you might have thought the change could not be spent before the transaction creating it was confirmed, but this is not the case.

I am not aware of any reason why reusing an old address for change would benefit a user, but the system will let you do it without it causing any problems.

In Bitcoin for privacy and security reasons users are advised to avoid reusing addresses, but this doesn't have any interaction with the kinetics of spending coins.