There are special formulations for special materials. There are offset inks and letterpress inks and screen inks, and etching inks. Over the years I've found that Van Son's Rubber Base Plus nicely serves as an excellent general purpose letterpress ink. You may be able to find some cheaper inks but Van Son is well worth whatever extra it costs. As a general rule, print text in black.
Black ink provides the greatest contrast between the words and the paper they're printed on.
This makes the best readability. If you wish to add a second color to your work red is probably the best choice, followed by blue, brown, and dark green. Fine printing uses color sparingly. Gaudy printing will detract from the message the words are meant to convey. Furniture, Reglet, Leads and Slugs Furniture is spacing material placed around the lines of type you've set to fill in the empty spaces in the chase of your press.