longarekel- good question.
First of all, if 4 is correct and you only wear one or two strings, you are not doing anything worse than not wearing techeiles. But if 1 is correct and you are wearing 4 than you indeed do loose out, as you are missing min kanaf. However, Min kanaf according to the rama is only a hiddur and is not meakeiv. Of course, If it is a mitzvah or a safek mitzvah than you are required to take a chance to loose that hiddur.
But regarding your question how do we know if we should go like shitas rambam or Raavad or Tosafos, obviously this is not a reason from stopping someone from wearing techeiles. Before there was a hachra’a in the machlokes rashi and rabeinu tam tefilin, it is poshut that somebody living then can’t say I just won’t wear tefilin since there is a machlokes.
So, what should you do?
Some people point out that most rishonim and most achronim are sosem like the shitah of tosafos. However, being that those achronim (ie mishna berura) are not clearly machria, and that it is brought down by the din of gardumim which tosafos will come out being the most machmir we cannot pasken based on that.
But by the way it appears, the gra is machria like the raavad in two places. So why should you go like the gra? Simply because most Poskim ( like Rav moshe and The Chazon Ish and the Steipler etc.) say that in something that you do not have a minhag in follow the opinion og the gr’a.
Ain kan makom lhaarich, but check out the tekhelet website or the tchelet-net website which have a lot of hock about this.