If you’re worried about fentanyl then get a test strip from a needle exchange. Also 0.1g is far too high when there’s both concerned about fentanyl AND you’re jumping in after a hiatus. I’d start with a really small dose.
With whether or not you can snort it etc it depends whether it’s a form that’s water soluble or if you need to add citric acid to it to dissolve. If it has a strong vinegar smell it might be more crude (in freebase form?) and require citric acid to dissolve in water. The vinegar is the scent of acetic anhydride which is the reagent that converts morphine to diacetylmorphine. Where I live we almost exclusively use ‘homebake heroin’ which is made from morphine tablets that have been reacted with Acetic Anhydride and often requires citric acid to dissolve. I believe it would be reasonably smokable in that case. But iirc no.4 is meant to be fully processed into he hydrochloride salt which would be water soluble - I just wouldn’t expect much vinegar smell - at least from the times I’ve had water soluble imported powder heroin