Games with Steam Cloud support may save games to Steam servers. You can see if a game has Steam Cloud support by checking if it has the Cloud icon beside it in Steam's Library List View. Unfortunately, even if a game has Steam Cloud support, that game may not save games via Steam Cloud and might only store things like keybindings or other settings. It also may not save all of your save games to Steam Cloud.
Even with Steam Cloud support, if you are using multiple computers it can sometimes take some time for all of your Steam Cloud settings and save games to synchronize with the server. Also, the save game support with Steam Cloud can be added as a late feature to a game after you've made a save, and that old save might never sync. I believe that if you are set in Offline mode, your games/settings won't sync until you go back to an online status in Steam.
Steam's Cloud icons on the Library List View will also sometimes inform you when there were problems syncing.
Torchlight, as an example, has provided Steam Cloud support only recently, and the support for full save games on Steam Cloud is even more recent. If your save games were created before the version with Steam Cloud save game support, those save games may not sync.
If you think that you are having Steam Cloud issues, your best bet may be to inquire with Steam's Support Forum.
Games that don't support Steam Cloud, or don't support saving games to Steam Cloud, will save games in "all the usual places", which means that it often varies from game to game, but is commonly in a folder under your Documents or Application Data folders. You may have to follow up with the individual game to find some of these save game locations.
Unless there was a specific issue with a game you purchased in Hong Kong being banned in Ireland, you should have no issues playing the games you purchased.. no matter where you go.
Issues come up when you install and use Steam on a different computer (authorizing that computer), although this is not a numbers game (steam doesn't limit the number of computers). This issue isn't common, but it has happened on rare occasions.
Issues also come up if you haven't changed/fixed your billing address on the credit card you use for a purchase, but that's not so much a Steam problem as it is a problem with not keeping up with your own addresses.
So... feel confident that you'll have no problem continuing to play Far Cry 3 and Dishonored when you are back in Ireland.
Best Answer
You can't.
You used to be able to do it, but due to fraud and currency exchange reasons, gift cards, like Apple/Google Play, are also region locked.
Instead, you are now encouraged to buy Digital Giftcards, which automatically convert currencies.
Yes, only if you switch your store location. To do this, simply go to your accounts page and select "Update your store country".
Only do this while you're in the UK.
This unfortunately means that any remaining wallet credit will be converted from euros to pounds, and some of its actual value may be lost due to conversion rates*. But on the plus side, the incoming money from your UK card will be 1:1 because it's the same currency.
*For example, if the rate is GBP:USD=X was 1.5, the effective rate that Steam will change Pounds into US Dollars will have a tax, so instead of getting $1.50 USD per pound, you'll only get $1.45 USD per pound. This value differs per currency and from minute-to-minute^.
You'll also require a local method of payment (ie. PayPal, Credit/Debit Card attached to a bank from that country).
^I seriously doubt that Steam will change its rates from minute-to-minute. AFAIK, it's more like daily.
Yes, it is legal. However, to stick with the Steam Subscriber Agreement, I'd recommend switching back to your home country's store after returning home from the UK, and to not use your Netherlands payment method (ie. credit cards) as it is against the SSA to purchase from a store that you're not in. (ie. US store from Australia, despite both using the same currency, and oddly enough - In Australia, we can choose to switch between US and AU stores)