I need as many rules on this card as possible.
If I summon it on main phase 1, can I use its effect in main phase 2?
How soon can I summon REB Dragon?

You can use Red-Eyes B. Chick's effect on the Main phase you summon it in since the effect does not state when you can use it.
Official rulings for Red-Eyes B. Chick on www.yugioh-card.com.

u can summon chick and tribute for reb dragon all in the same main phase just like how u can use hand of nephytys or exiled force as soon as u summon them

True and if you have REBC, REBC and REDD in hand to you can on my main phase summon REBC, then sac it to SS REBD, and sac REDB to summon REDD.
I abused the Hand special summoning by using its effect and same for Kaibaman for BEWD (when i ran BEWD)