The more I read about it, the more I'm frustrated by the options, and I'm thinking about things like sealer, washcoating, grain filler, etc.
This is part of the problem with finishing when you're starting out, all the many options. It's the same starting out in most areas, where you have to learn about lots of things knowing that eventually you'll use just a handful of them 95% of the time.
There are a great many options available and numerous combinations possible on top of that but I know a couple of woodworkers online who use wiping varnish for virtually all their pieces. And I've read on one furniture maker's blog that he uses nothing but linseed oil on his work, saying that if it was good enough as a finish for hundreds of years it's good enough now.
I'm going for a more uniform appearance, with grain showing of course, but I'd like to de-emphasize the grain
If you want to truly hide the grain on oak and produce the most even colour possible then a full grain fill is the way to go but this is a lot of extra work. You can go a lot of the way there just with the right colouring product.
This is the classic case for picking your colouring product with care as what is sold as "stain" is a number of very different things.
Types of "stain"
There are two main classes of stain, pigment stains and dye stains, and they work completely differently. A pigment stain has actual pigment particles (large) suspended in it while a true stain is coloured by dye (very tiny). With pigment stains those particles naturally collect in recesses, actually increasing the contrast and making the grain stand out. Dye stains on the other hand colour the wood fairly evenly so have a natural tendency to reduce the contrast between the recessed grain and the surrounding wood.
There is also something called "gel stain" which isn't strictly a stain at all. It is coloured varnish that has been artificially thickened slightly.
So it's definitely dye stain you want to use here. Get a dye stain or two in likely colours and experiment with them until you're confident in how to apply the product evenly. For your final finish I would recommend wiping on varnish.
I've read good things about oil/varnish blend and about wiping varnish.
Those are both fine in their respective ways and for appropriate applications. They both have the same basic advantage, that of being wipe on finishes but wiping varnish is a better finish in a few key respects, being more flexible in how it can be applied and providing better waterproofing and scratch-resistance.
Make your own
In case you haven't come across this before wiping varnish is just normal varnish thinned slightly. As with "wood conditioner" you pay too much for the commercial variety because they're charging you through the nose for mineral spirits, which is cheap. Better to make your own since it's much cheaper and you can have full control over the level of dilution to suit your own preferences and the weather conditions (the same dilution won't equally suit finishing during summer months and on the coldest days of winter).
All you need to do is take a clean jar and pour in some (gloss) varnish, then add 1/3 or more spirits, shake the jar and you're good to go.
Oil/varnish blends can be made in exactly the same way, usually beginning with a simple 1:1:1 mixture of BLO, varnish and spirits.
Note that shaking a finish is usually discouraged just prior to use because it introduces bubbles but they're irrelevant in a wipe-on finish because the application process will naturally pop any bubbles.
Of course I'll make multiple samples of all the potential processes
That's good. Wood varies a surprising amount sometimes and not least in how it takes finish. So it's vital to do test boards to assess how any finishing regimen will work on your wood.
