Kaz pretty much laid it out well. I would only add a few points according to a few of your questions. 

What about the point that the golf-tube arrows can easily be knocked out of the air by most spearman?
-----Yes, the tubes do fly a bit slower so they can get knocked out of the air easier. Tacticlly, I simply adjust to fighting as far up in the line as possible to take out targets just outside what ever the minum distance may be for the war. (for a 10' rule just stand by a spearman to judge my range) This way my targets have little chance of stopping my arrows before they hit.

Umm. You have been doing it for a while. What about the new archer? Can they easily make arrows using just the rules for them?
------The tube arrows are very easy to make. The trip to the store to buy siloflex, tennis balls, and tape is more difficult than buying. And as already pointed out the instructions are very simple to follow. With a band saw, drill, glue gun, and a few sets of helping hands; we could crank out bushels of arrows pretty easily.
Can you use the same bows (and crossbows) for both golf-tube arrows and target arrows?
------You can if you want to, but I would advise against it. Bows are a tool so it's best to remember to have the right tool for the right job. What you use for target shooting you'll fine tune toward target shooting. As with a combat bow which will be tuned for CA. Plus, what ever bow you take onto the battlefield you have to be ready to loose to damage. I use an old Bear recurve I found cheap with the aforementioned enlarged shelf. I have it strung for 45lbs at a 28" draw. If it gets broken on the field I'll still have my long bow for target. Plus, I won't be too upset about it since I only paid $45 for it about 10 yrs ago.