If it's powder (ecp/#4) it will dissolve immediately. It's very water soluble, and you don't need a lot of water, so you don't need the 3 ml syringes. If it doesn't dissolve, what's left is cut.
On this board, yes, I hear about people using micron filters. IRL, in over 20 years on and off in the dope game I never saw someone use one. Although from what I gather it's more imperative to use when shooting pills due to fillers and binders. (NOTE: I am not saying micron filters shouldn't be used for dope. I'm sure they lessen risk a lot. I'm just saying in my *personal* experience I've never seen anyone use one for dope. Most heroin addicts can barely afford a new needle once they get really bad, I've seen people with no cotton use lint from jeans...).
But yes if you don't have the micron filter just use a really small piece off a Qtip rolled up tight, and draw up thru that. Basically--like you said. Powder in spoon, add water, dope dissolves easily--just mix around with the plunger from a different syringe, add cotton, draw up...
And yes do less than you think you need on first one. Test shot, if you will. It'll be easier to gauge strength as that's what we can't tell you over the Internet