I seem to have gotten my bow down rather thin in the limbs and it seems to look symmetrical.  I say seems, this is my first time building one.  I can bend the limbs some by hand, so they're definitely in the area of where I think I'd need for a draw weight.

I've seen long string tillering, and I can build the tree for that easily, but do I need to use a real bowstring, or can I do that tillering with anything?  I ask because I haven't been able to sell enough stuff to buy a string for it yet, and dunno when I can sell another knife or powder accessory (I've been seriously slowed down in making because of new trailer utility hookups and general sickness.)  

I've seen a lot of mention of linen bowstrings around the net.  I might could get linen around here.  I know it was used with English longbows, and they had ridiculous draw weights.  If I did a loop on one end and a timber hitch on the other, could I use the same string for long string and shooting, or would I need to change strings anyway?

I know I'm full of questions.  If I get annoying, just tell me to shut up.  Most people need to eventually.  Ask my wife.

I use a long string after I complete the floor tiller stage; about 4" of tip movement and both limbs are bending evenly and together.
A 1/4# spool of B-50 is about $9 and make lots of strings with it.
You can use any strong cordage for a "long" string. It only need to be slightly longer than the bow. I sometimes use para cord for a tiller string.
Once I get a bow stave to low brace I make a string for it and complete the tillering with that string.

There are buildalongs on my site that will answer your questions probably.
Jawge
http://georgeandjoni.home.comcast.net/~georgeandjoni/index.html