There there, no need to get worked up :) Learning a language can be frustrating at times. The more you persevere, the better your progress would be. Each day you come closer to being better at it :) "If it could be done, we would/could have a major success" is correct. Other ways : "It would be a major success for us if we could do it" "It would be a major success for us if we manage to do it" "If we are able to do it, it would be a major success"

This is especially fun and exciting... subjunctive [...be done] PLUS second conditional [predicting results ("...a success") of unlikely future actions (the "it" in "if it could be done"] YOUR QUESTION: "Is it right? REPLY: It's hard to say conclusively... Your question should be: Am I saying what I want to say? The form seems correct. However, I am not 100% sure WHAT YOU MEAN. There is some vagueness regrading your subject i.e. what is the "it" in "If it could be done..." There is no MEANING outside on context, especially when you are swimming so deep in the oceans of grammar that you're using the BE VERB in subjunctive form, in a conditional sentence. Working on / generating perfect grammatical sentences is an academic exercise that can lead to more confusion that clarity because form only exists to express MEANING.

Okay -- cool. Here's your sentence: "If we could maybe do this one more thing, we would make a huge success." Simply put, If we do this, we will be successful (definite result) For more uncertain results, a "conditional" result, depending on the outcome of the first action / verb... If we could do this one thing, then we would be successful. If we could do this one thing, then we would have success. OR If we were able to do this one thing, then we would be successful. If we were able to do this one thing, then we would have success.

kill me now, subjunctive mood bitch ... omg ... grammar should never be taken THAT seriously :-)

yes it is, if it could be done, we would have much success