Welcome Afgos; I've made a number of all-bamboo bows with draw weights from 20# to 50#. You want a culm that is not this year's new growth, but last year's mature growth.
You'll want a culm at least 4" (10 cm) in diameter with as wide node spacing as you can find. Ideally you want the handle centered for or less between two nodes.
You want to split the culm and use the inside of the culm as the back of the bow, with the curved outer skin as the belly of the bow facing you -- the outer rind works best in compression.
Then you send the split down until you get a "plank" about 2" (5 cm) wide, flat from end to end on the belly (inside). Then you shape the plan view of the bow -- bend-through-the-handle designs like the classic flat bow or pyramid or Mollegabet shapes work best.