Drug info - Advice for a heroin novice

[baron samedi]

SWIM recently bought his first bit of smack. Although he is on a methadone script and has experience with opiates he has never even dabbled with this particular drug before, so needs some advice. He bought it off someone he didn't know very well, and didn't want to let on that he knows very little about this particular opioid (in terms of first hand experience), in case the person in question thought he could be easily ripped off. The person he bought it off is very dodgy, to put it bluntly.
Anyway SWIM needs advice as to what kind of smack he has, the best way for him to take it, and what dosage he should use? He lives in the UK, so probably SWIMMERS who live there too will be best qualified to answer some of these questions.
Firstly, he needs to know what grade he's dealing with. The smack in question is a very, very light brown powder, almost white with a hint of brown in fact. SWIM was actually expecting something very brown in colour, which he thought was the most common type in the UK, but maybe he has read that a lot of smack in UK is now better quality "white" heroin, so hopefully he has some of that. Of course, there is the possibility that it is not heroin at all, but without anyone to actually confirm this for SWIM, he has no way of knowing. His instinct about the way the deal was done is that it IS heroin, but he could be wrong. From SWIM's description of the colour can any SWIMMERs tell him what grade he has?
Secondly, he has no intention of injecting the stuff, so he needs to know the best way of taking it i.e. is he better off smoking or snorting? He was under the impression that the very dark brown stuff which used to be most common in the UK, could not be snorted, but if he does indeed have a higher grade, maybe this stuff can be. If not, can anyone tell him how to "chase the dragon", step by step, or direct him to an appropriate thread?
Thirdly, the dosage. SWIM knows full well there is always a danger of OD'ing, especially for 1st timers, like himself, so he's got to be careful, especially if it's strong and because he already takes methadone daily (35ml, soon to be 45). How much should he start off with, given his circumstances? He does not want to waste it as he doesn't know when he'll next be able to score some.
SWIM will strongly appreciate answers to these questions, and I will pass them on to him, in order to reduce any harm, that using such drugs might cause him. Thankyou!