Lilmod, who says that an Ashkenazi may not rely on a Sephardi posek and vice-versa if the question does not involve a machloket between the Rema and the Mechaber? Who is a legitimate posek? As for leniences, to paraphrase Rabbi Shay Schechter in the name of his father, if you can find one in a popular halacha book grab it and run. They tend to be as machmir as possible to avoid being attacked. Not to mention the fact that avereichim tend to be machmir anyway. I heard that one avereich asked Rav Eliashiv a question for his book. When Rav Eliashiv was lenient the avereich argued with him so RE told him “If you want to be machmir don’t do it”. The avereich wrote that RE said that it is worthy to be machmir.Oe should also check the footnotes and look up the sources. For example, after the first edition of Shemirat Shabbat K.Hilchata was attacked Rav Neuwirth put out a new edition with the chumrot in the main part and the kulot in the footnotes.
In the case of a machloket where there is more or less an equal number on each side, if you cannot clarify it with your rav there is a simple principle. If it is a Torah mitzva be stringent, if it is a rabbinic mitzva you can be lenient. However, sometimes one can rely on a leniency regarding a Torah mitzva in special circumstances (great loss or need, b’diavad, etc.) There are no crutches. You have to learn thoroughly just to be able to get out of the level of the son who did not know how to ask a question.