Is it possible to change the size of org-mode-agenda on opening so that when opening the agenda, it doesn't open so large (saving me having to resize it)?
I am using org version 9.0.8 and for me there is "org-agenda-window-setup" and "org-agenda-window-frame-fractions". You need to set org-agenda-window-setup to reorganize-frame and then fractions to something that fits you.
In addition to what Matthias said, you can control whether the agenda opens horizontally or vertically. There are two threshold values
split-height-threshold by which org determines this automatically, but you can also force it; here's what I have in my
.emacs so that the agenda always opens vertically:
;; Open agenda vertically by default (defadvice org-agenda (around split-vertically activate) (let ( (split-width-threshold 40) ; or whatever width makes sense for you (split-height-threshold nil)) ; but never horizontally ad-do-it))