If it is a common plec, he can grow to 24 inches. But not in that tank! He needs a new home, and soon, before his health is affected. They may seem very cute and small at first but they can grow quickly and produce a lot of waste, which will put a strain on your filter and risk the health of your other fish.
According to the website calculator I use, 96 ltrs is 25 gallons (but it will be a little less with displacement).
Assuming that the pleco is out of the equation, this is how I work out the rest of your stock:
2 3-spot gouramis= 2x 5" = 10"
3 mollies= 3x3" or 3x5" (depending on type of molly)= 9" or 15"
2 black widows= 2x2.4"= 4.8"
2 white-tips= 2x2"= 4"
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so either 27.8 or 33.8
Either way you will be overstocked, even not counting the plec, once these fish are fully grown.
The other problem is that you are keeping two types of schooling fish in pairs (the two tetras), which is not ideal for their wellbeing. It means they are under permanent stress, and can also mean that the stronger of the pair ends up bullying the weaker member (we get a lot of posts about this type of situation!). Black widows can also show a tendency to fin-nipping when kept in small numbers- so keep an eye on your gouramis!
At this point you need to ask yourself not what will look most attractive in your tank, but what will be the best solution for your present fish.
Rehoming the plec should be a priority. Then some sort of way of upping the numbers of the tetras- but unfortunately you can't just go out and buy more fish, because it might crash the tank. Could you rehome one gourami? Or maybe it could be done by adding extra filtration.
I would watch the situation with the mollies and the gouramis quite closely too. You have a situation where big greedy fish are at the same surface level as big potentially territorial fish (the gouramis). I can see this part of the tank getting more crowded than might be good for the fish. Which reminds me, are your gouramis a pair (as in 1 male, 1 female)? Check that out, as keeping two males in a relatively small tank might cause trouble.