How do I avoid streaks or elevated lines when I wipe off the Good Stuff? Should it be thinned somehow so that the gel will settle onto an even plane? I do not have a problem with the initial coat as it mainly gets absorbed by the wood, but coats 2, 3 and 4 usually are not smooth. I've sanded with 400 which does remove some of the elevated areas but not completely.
Should it be thinned somehow so that the gel will settle onto an even plane?
You can do that but it negates the advantage of using a gel varnish in the first place.
How do I avoid streaks or elevated lines when I wipe off the Good Stuff?
coats 2, 3 and 4 usually are not smooth
Type of cloth may make a difference
The type of cloth you use may have a large effect here so you should experiment and see what works best for you. Over the years I've seen recommendations for cheesecloth, old sports socks (clean!), pantyhose/tights wrapped around a cotton cloth, quality paper towels, lint-free cotton such as from old sheets or T-shirts and last but by no means least, microfibre cloths.
Note: I would recommend always wearing gloves for this part of the process. Regardless if you're okay with cleaning varnish off your skin afterwards and no matter how tough and gnarly your hands are :-)
Wipe until it's done
I don't use gel varnish much but what I've found is you should continue wiping until you don't have elevated lines, which can be quite a race when it's warm and you have a fast-drying product!
This does involve wiping away more of the product than you really want to (because that's all wasted) but it's the only real alternative to sanding the surface afterwards which I try to avoid. To prevent excessive waste I try to apply the minimum amount to begin with*.
That said, sanding the surface afterwards IS a well-established way of perfecting the surface of dried finish, to make it dead flat and also to achieve a specific sheen (i.e. going from high gloss to any level of reduced sheen).
I've sanded with 400 which does remove some of the elevated areas but not completely.
Sand further. When you're sanding to remove an application defect, you keep sanding until the surface is as uniform as it needs to be.
Would applying paste wav using 000 steel wool help smooth out the finish?
Yes a little but, but you should only do this once you're sure no more varnish is going on as the wax would interfere with adhesion. Also, steel wool (and other conformable abrasives) are best at giving a uniform sheen, not at cutting back which is the stage you're still at.
*Same as when applying BLO or wiping varnish where I never flood the surface. Even though this is fairly common advice it merely wastes finish and should only be done when speed is essential — subsequent coats will achieve the same end without tons of finish ending up soaked into rags that are going to be thrown away.