RaspNode has a good way of getting started for the RaspberryPi.
Your steps, assuming you've configured it for networking, are:
Downloading and installing dependencies
Downloading and installing Geth
Configure and run Geth
Configure home network to sync up with
the Ethereum network
Arduinos and other microcontrollers don't meet the hardware specifications ...
so when we (me and the ShaneT) implemented hardware signing (private key stored exclusively on AWS CloudHSM) there were a number of things we learned. Hopefully this gives you a guide on how you can achieve it. Unfortunately I can't directly share the code as it's my firm's IP.
Here is the actual tx we first made using AWS CloudHSM on mainnet :)
There is no single API that will fetch all the tokens held by an address. This is because that data exists over different contracts.
To know the holding of a particular token by an address you have to query that contract. Similarly for all the other tokens. You can fetch one by one all the balances you are interested in.
Again, new token contracts are ...