Question: I have just discovered that you can do both a combined smart contract that includes both the token and the crowdsale OR have the token in a separate contract from the crowdsale contract.

Can anyone tell me what the advantages are to either of these methods please?

Many Thanks,

Phil.

Answer: 
If your contract costs that much, then you must be doing a bunch of storage initialization. Storage, by far, costs the most to read/write.

The irony of Solidity is that it costs less to redo things in memory, so if you have some variables, you can re-initialize and recalculate. It's probably better to do so in memory each time a contract method is called.
My approach is:

1. Deploy to a testnet like ropsten and note the gas used
2. Go to <https://web3-tools.com/> and type in the gas to back-calculate the gas required in USD

Like the accepted answer, my basic contract was about 1,400,000 (compared to 21,000) for a transfer

Disclosure: I wrote web3-tools.com