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Will lower fee delay the transaction? can fee be set to zero or is there a minimum value? if there is a minimum value than how is it different from existing wallets?
Depends on a lot of factors...
If your transaction is a high priority transaction***, you can try not to add any fees... Altough most miners will not add your tx to a block without it having a fee, there are still some good samaritans that add zero-fee high priority transactions to their blocks.
For everyone else, there are sites like this one:
https://bitcoinfees.21.co/1) estimate your transaction size (in bytes, NOT in satoshi's)**
2) multiply by the number found on
https://bitcoinfees.21.co/ , it's your own pick if you want the transaction to have a high probability of being added to the next block, or if you're willing to wait a bit longer.
Long story short: it depends on the size (in BTC) and age (in confirmations) of your inputs to determine the priority. If it's high enough, you can try a zero-fee tx, but it can take a long time to confirm.
If you can't create a high priority transaction, you should add a fee, how much depends mostly on the number of inputs and outputs of your transaction. Adding to much won't help you a single bit, adding to little might slow down the first confirmation, adding exactly enough would be ideal
BTW: i don't quite get the last part of your question: "how is it different from existing wallets?". I'm saying the OP can run bitcoind and use a json-rpc connection to create a transaction. Bitcoind is the "original". It's usually installed together with bitcoin-qt and was the first wallet. bitcoind is also the daemon that is ran by the nodes everybody relies on
** size can be estimated by: [number of inputs]*180 + [number of outputs]*34 + 10
*** priority = sum(input_value_in_base_units * input_age)/size_in_bytes
high priority = a priority above 57,600,000
source:
https://en.bitcoin.it/wiki/Transaction_fees