Hello and welcome,
First of all, you can definitely install a Bitcoin node and the plugin on a Windows PC for testing purposes. If you wish to actually set up a website you will probably need to install everything on a hosted server (which would usually run Linux). It is theoretically possible to run your website from your Windows machine, but this is not recommended. You would need a static IP, a UPS, a good backup mechanism, configure firewalls yourself, etc. This is why I demonstrate installation on Linux (not Mac).
1. If the wallet is on the same machine as the PHP server that runs WordPress, then you should use the local loopback address, 127.0.0.1.
2. You do not necessarily need to use the shell to create the configuration file. You can use any means, as long as the file is in the right place. For example, you can save the file using Notepad at %APPDATA%\Bitcoin\bitcoin.conf. The shell variable %APPDATA% will point to the correct directory for storing application data for your current user. (See also https://support.pointlogic.com/faq/troubleshooting/accessing-the-appdata-folder)
The location of the Bitcoin data directory (and hence of the bitcoin.conf file) is detailed in the bitcoin wiki: https://en.bitcoin.it/wiki/Running_Bitcoin#Bitcoin.conf_Configuration_File
I am not sure why the core wouldn’t start, but know that all error messages get written out to a log file, so you can check them later. The log file is in %APPDATA%\Bitcoin\debug.log. If you find the error message, you can google it or post it here.
3. Even before the blockchain finishes syncing, you can try to setup the RPC settings. When the settings are correct, you will see a status of “Syncing” rather than “Responding” in the coin adapter status (“Wallets” -> “Adapters”). You would still need to wait for the sync to finish, before you can actually perform transactions.
4. The Exchange extension is NOT like localbitcoins. Instead it is more like bittrex or poloniex, i.e. it allows you to create market pairs where users can enter market and limit orders in an order book. Limit orders can be thought of as offers to buy or sell. The whole trading process is online, it does not involve actually meeting locally, like localbitcoins does. Localbitcoin can be used globally and is well known and established, so in my opinion there is no point in you offering a similar service.
5. The markets that you create with the Exchange extension have their own orderbook, and thus their own prices. This is also true of all major crypto exchanges. Prices sync between exchanges via user action, because when they do not, arbitrage opportunities arise between exchanges. Arbitrage traders will balance out any price differences, and they profit from users who place orders away from the current price. Thus users are incentivized to place orders around the actual price of the cryptocurrencies they trade. There is no liquidity “magically” imported from elsewhere: users need to place orders in your site for a market to exist and for price discovery to work. This is a full exchange where you have full control. You can also specify maker and taker fee percentages.
If you simply need a frontend for other exchanges, use the ShapeShift extension instead.
Hope this helps. Please let me know if you have any further questions. If you have questions about the Exchange, please post them at the support forum for the Exchange extension.
with regards