All depends on what you want.
My own amazon have about 50% block, due to thunderstroke needing quite some dex anyway (151). She have some LL with a bk, which helps.
Don't forget that allot of typical amazon items give a high amount of +dex.
A raven gives a maximum of 20 dex. (you can use 2)
A cat's eye (which i see commonly used) gives +25 dex + 20 ias
Titans revenge gives +20 dex (but also needs 109 dex to use)
I see here 20+20+25+20 = 85 added dex.
You need 109 dex for your titans (asuming you want to use one). 109-20-20-25 = 44 points that need to be stat in it, taken in account you have an random torch, giving 14 points, it dropts to 30. Minus the 25 dex you start with on an ama, you have 5 points you need to spend in dex to wear titans. Titans add 20 dex, giving you a total of 139 dex, for spending 5 points.
If you dont want to use cat's eye, but highlords, you can think about using waterwalk's as an addition. Which adds +15 dex. In that case, it'll cost (5+25-15=) 15 instead of 5 points in dex you need to add.
Every point added in dex, cost you 3 hp, if you dont have any items adding life. So, 15 dex would cost you (15*3=)45 life. However, if your chances of block are high, you need less of it too.
Its all about balancing out, my old (nearly perfect) ama has:
60 ias = faster attacks = more dmg.
41 fhr = faster recovery = saver
43 dr = taking less dmg
10 ll = recovering from damage more fast
50% block = quite enough on an ama
75-75-85-75 res = what matters allot on hell, you cant block / dr elemetal dmg
11k charged strike, 12 bolts
4.4k fury, 51 bolts