Can someone who is not Jewish but is seriously considering converting observe Shabbat? Here I specifically mean home observance (Kiddush, etc.). Also, can a non-Jew looking into converting pray Jewish prayers? I'm coming from a Reform viewpoint if that makes a difference.
In either January of 1984 or April of 1983 (I can't tell because of the format of the book online) the Reform Movement published a responsum (#165) about whether a non-Jew may light Shabbat candles. In the responsum, they state that while it is technically problematic for a non-Jew to say the blessing which includes "... who sanctified us with his commandments," doing so is seen as a "positive indication that the home is to be Jewish."
The non-Jewish spouse's participation in the Friday evening ritual at home has evolved naturally. Frequently she does light the shabbat candles and through this indicates a wish to establish some ties with Judaism at home. Technically, of course, it is inappropriate for a Christian to recite the traditional benediction as it contains the words asher qidshanu - "who sanctified us with his commandments," which indicates an obligation imposed on Jews. We have, however, taken this act as a positive indication that the home is to be Jewish.
The responsum goes on to say that the same logic cannot be extended to synagogue services. "[N]on-Jews may not lead in essential segments of the synagogue service or sections which utilize such phrases as 'who has sanctified us.'"
Since your question indicates that you are specifically asking about home observances, I think it is can be understood that from the position of the Reform movement you may participate as you wish.
You may certainly do the prayers and make the kiddush.
It would be best if you're still doing something that's not Sabbath-observant at some point in the day. (E.g. drive a car, or light a fire.)
Good luck with your journey! At some point you should be able to determine if you want to go all the way to conversion, or if not, then Shabbat is not for you. (But feel free to borrow freely from Jewish prayer texts if it suits you.)
In Reform Judaism, you don't need to not observe Shabbat. Do what you think is most meaningful to you. If you don't intend to become orthodox, there's not really a restriction on Shabbat.