1.) Tungsten powder is not the best way. Leads to using too much epoxy which usually goes up the shaft. Tip weights are used by every OEM now. I really like using lead tape. Tip weights do NOT affect flex. Too much substrate (tungsten, beads, sugar, whatever) in the epoxy can weaken the epoxy and lead to problems.
2.) Really hard to get to an exact swing weight which is why I like lead tape, Then it is easy.
3.) If there is an option, you should always used long cure epoxy. Short cure epoxy is usually more brittle and doesn't have the elasticity of a 24hr cure epoxy. If need be, you can heat cure a 24 hr epoxy so that it cures in under an hour. Typically long cure has greater shear strength.
4.) You can get the epoxy out of a shaft without taking off the grip. I use a long piece of brass rod that you can insert into the vent hole. The drawback is that sometimes it doesn't work and then you end up cutting off the grip to get the rod out.
5.) Length of the club changes the amount of weight needed to achieve one SW point. Takes less on a driver than it does on a PW.