I'm afraid that won't work.
Firstly there are soft water (barbs, gouramis) and hard water fish (platies) on your list. One group or other won't be happy. Can you find out your water hardness, please - if you are on mains water, your water provider's website should tell you. You need a number and the unit of measurement (there are several they could use).
Secondly, tiger barbs are one of the nippiest fish in the hobby and it is very difficult to find tank mates that can cope with them. The long 'feelers' of gouramis will probably be bitten off.
If it's the looks of them which appeal to you, five band barbs are similar but without the nippiness - provided you have soft water.
Lastly - how are you cycling the tank? Are you adding ammonia or have lots of fast growing live plants - or just letting it run?