Looks like you have learned a valuable lesson, pet shops just want your money. The advise you can get from experience fish keepers online is free. Just ask before you make the mistakes.
To answer your question 32ltr is suitable for 0 guppies. A betta maybe, shrimp maybe, not guppies. Even if you got the males to females ratio right you will quickly have more baby guppies than you can count! Thats a whole lotta guppies in 32ltrs of water!
To give you an idea tho, many moons ago i had a 35litre planted nano tank and kept 1 fancy betta, 6 harlequin rasboras and a ton of breeding cherry shrimp, it was a joy to keep and looked stunning with all the plants, literally like a jungle! Another option which would require research and help from forum people is a dwarf puffer fish set up.
Like others have said a tank must be cycled before adding fish, usually takes 2 - 6 weeks for the good bacteria to grow in your filter.
Also you say suckerfish, what is a suckerfish? Im guessing a hillstream loach or a pleco of some sort, either way one requires a very specialised high oxygen set up and the other could possibly grow to 60cm long, either way both are unsuitable for 32ltrs!
When you are at the shop you need to find out and write down the fishes scientific name, then go home and look it up online and ask questions on forums before you give them your money and end up with a dead fish, they know you'l keep coming back for more!
Sorry the pet shop stitched you up, hope you get your tank on track!
edit: you said you got a suckerfish to clean the tank. Thats your job as a fish keeper to do the tank cleaning, the more fish there is the more mess there will be and the more work you will have to do to keep it clean. This shop really took you for a ride!