is there any minimal threshold for initial purchase?
That would depend on the exchange. Bittrex used a minimum of 0.0005 satoshi.
If you go to efl.nl, our online wallet service, and you give your wallet a name, you receive 0.0001EFL. Transactions are free so you can spend 1000 times one EFL-satoshi to play with.
It all dutch for the time beeing, but I think you will get the message. (betalen=payment; ontvangen=receive)