What length Jo staff is most popular for Aikido practice? Also, what to look for if looking at buying a metal sword? All around, to display, maybe practice some.. etc. Not a real high dollar one, something mid range.
I've seen a wide variety of weapon styles and builds used in aikido dojo. Not knowing what sort of practice you'll be engaging in, here's some general advise:
Bokken / bokuto
If your training is going to involve heavy/hard impact against other weapons, invest in a high-quality bokuto with proper grain structure. Shiro kashi (Japanese white oak) is a common choice (good value). American hickory is also highly recommended for hard impact training. If your training is going to involve power-building exercises and a lot of suburi, get a bokuto that feels comfortable in the hand, is well balanced, and is hefty (to give you a bit of challenge as opposed to too-light a training instrument). If your practice involves the use of tsuba, make sure the bokuto is designed to be fitted with one (usually a transition or nudge between tsuka and "blade"). If your training involves kumi-iai (paired iai), the common plastic saya available from vendors only fit certain types of bokuto.
I'd recommend against laminated construction. Also, it's best to buy a longer jo that you can always cut to your teacher's or style's specification. White oak, hickory are also good jo materials, although there's always the array of exotic woods to choose from (depending on your budget).
Iaito / Shinken
If you plan on training with a live blade, please get yourself some proper instruction first. If you're going to practice iai as some aikido schools do, get yourself a properly balanced katana -- some (most) of those cheap shinken people use and recommend are poorly balanced and/or don't have enough sori (curvature) for iai training. So, a good iaito (non-sharp alloy blade) might be a better investment. Keep in mind that depending on where you train, a live blade might not be allowed or practical (certain state facilities, or travel into certain countries, or training in crowded rooms), so a iaito would be better suited. Training with a live blade is fundamental to heighten the seriousness of training, but only when it's safe and practical to do so. If what you're interested in is chopping rolled mats and such, the cheap shinken would do the trick; in my personal view though, I think this practice has little bujutsu value.