I'd use it all. Do two fast rinses and then let the leaves stand (dry) for a minute or so to let them bloom a bit. After that start your steeps. The first few should be instant. Water goes into the gaiwan, stir once with the lid, pour. If you go any slower you'll just get sludge.
You could also separate the sample into halves and brew them longer, but I think that many very short steeps is usually better. If you go the 3.5g route, I'd still pour off the first steep instantly just to see how strong it is. If it's weak go to 10-20 sec for the second and so on. Shu puerh infuses very quickly for the first few brews and usually tastes better a little on the thin side than over brewed.