Alone (μονος). Predicate adjective with ο αρχιερευς.

Once in the year (απαξ του ενιαυτου). Once for each year (not ποτε, at any time) with genitive of time.

Not without blood (ου χωρις αιματος). According to Leviticus 16:14. Not even he could enter the second tent (Holy of Holies) without blood.

The errors of the people (των του λαου αγνοηματων). Late word from αγνοεω, not to know (Hebrews 5:2), only here in the N.T., but in LXX, papyri, and inscriptions where a distinction is drawn between errors (αγνοηματα) and crimes (αρμαρτηματα). In Genesis 43:12 αγνοημα is "an oversight." But these sins of ignorance (αγνοηματα) were sins and called for atonement. See Hebrews 10:26 for wilful sinning.