on the gybe, you are correct in that you don't want to lose a lot of boatspeed. This can cause a nose-dive when the main flips to the new side and powers up.

Keep the boat moving as best as possible, and make the gybe smooth and relatively quick. Don't head up too high after the gybe or you could face a knockdown, just head high enough to ensure you're on the new gybe and maintain most of your entry boatspeed. As the TWS increases, your gybe angle will decrease.

If you look at some boat wakes, you may even see a slight "S" turn as the boat enters the gybe, passes clew to wind, heads up (maybe 140 degrees to TWD) and gains speed, and then drives down slightly once up to speed.

The spinnaker helps keep boatspeed through a gybe. In light air, you can "float" the spin through the gybe, keeping it full throughout the transistion from one side to the other. In medium and heavy air, the turn is usually too quick to worry about it and you just focus on trimming to the new heading.

Without a spin, it helps to sheet in the traveler while steering through the gybe (to prevent a huge swing of the boom) and immediately ease it out on the other side.

As far as crew positions go, in the gybe you want to try and stay as far back as practical to prevent nosing in to the back of a swell and stopping the boat. In moderate air, it is typical to see crews prepare for a gybe by driving down and coming off the wire to "organize" for the gybe so they may resume quickly on the new heading

Your best bet, however, would be to sail with a more experienced boat and watch how they do things. Or you can sail with one of their crew for individualized instruction.