This is where my tech knowledge of the blockchain starts to fail me. So what determines the size of a tx? Isn't it the sum of vins + vouts?The "cost" for the blockchain is the actual size of the transaction - the larger your tx the greater the "cost" (the fee). To account/predict tx fee you need to calculate the size of the raw tx. You can try to get into blockchain for free (there is a small cap for it) but keep in mind that there is no incentive for miners to include such txes so it might never be included in blocks at all.
So if you create a feature to consolidate all your inputs after each tx through a persistent change address, every subsequent tx will have a much lower kb weight
Obviously this has other implications and not ideal for all, but just trying to figure this out.
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