Best timing for Post Bacc Courses

[galaxyx]

I'm currently doing an informal post bacc and I will have all of my basic sciences done by this summer. I would like to take biochem and some other upper division sciences next year for letters of rec and to show that I am capable of the course load since I've been out of school for 8 years. At my local school, Biochem is only offered in the spring, so would it be better to take two part time semesters of upper division sciences, or take no classes in the fall, and take a full load in the spring? I don't need GPA repair so the added cost of two more full time semesters doesn't make sense and I just don't have the money. I have the savings for one more full semester after this one. Has anyone had any trouble getting LOR in their last semester before applying? Basic sciences here have over 100 students in every class so I'd rather get letters from upper division classes than the current classes I'm in.