I'd want a stiffer rear spring if you're carrying much on the back... at a minimum, crank up the preload some, but a stiffer spring is the right way. Adding weight out back does something to the front, but not a ton. If you won't be doing all that much loaded up touring, I probably wouldn't bother with the stiffer springs but if that's all you plan on doing you should.
There's always some blowby past the rings, although the better they seal the less there is. None are perfect. One of the components of blowby is unburned fuel. Water is a byproduct of combustion, so there's some water in there too (at first as water vapor). The more cold starts, the more contaminants end up in the oil.
A typical car or streetbike will have a thermostat, preventing much coolant from running through the radiator unless coolant is warm enough - 180F is a fairly typical number. However, the WR and YZ don't have a thermostat, so they run at a temperature based on heat production and cooling capacity. On trails, you're using a fair amount of power and not going that fast, so you need a reasonable amount of cooling capacity to not overheat there (and WRs are fairly good about that, they have a lot of cooling capacity). Around town, there's usually not that much airflow, so they usually run fairly warm there too. On the highway, I've read they typically run around 60F above ambient temperature, with oil around 10F warmer than coolant. Sunday I went on a fairly long ride (200mi, with minimal stops) on my WR supermoto, in fairly cool weather (60F). I started doing around 60 miles in the hills, then had to hop on the freeway for 5 miles to get to the next fun road, and went to a gas station as soon as I got off the freeway. I'd read about overcooling before, so when I stopped I took off my gloves and found that I could hold my hand on either my cylinder head or my radiators without discomfort.
Running cool does have some upsides: if you then get stuck in traffic (or are stop and go for a while for some other reason), it'll take longer for you to overheat. I'm installing a fan when I install the thermostat for that reason. It also heats the air up less on the way in, keeping it denser so you get more air, which can help power. However, it also has downsides. With the oil cooler, it won't evaporate off water or gas as quickly (if at all), so they'll end up staying in your oil. Water and gas both evaporate a lot faster at 190F than 130F. Additionally, oil gets thinner as it warms up, so cooler oil results in more drag and less power.
On most bikes, sustained moderate speed is about as easy on oil as it gets, as it keeps the engine cool enough to not cook the oil as well as warm enough to evaporate water and fuel out. The same isn't always true on WRs. It's possible that it's warm enough where you are that the engine never runs cool enough to be problematic. I might be making a mountain out of a molehill here, though, especially somewhere with warm weather.
I haven't done enough touring on dual sports to say what the best options are. ADVRider has quite a few people who do, so I'd look for ideas there.
When you say "lowering the front suspension in the triple clamps", what exactly do you mean? If you lower the forks in the triples (push the forks down), that increases front ride height and therefore rake and trail. Stability is typically increased, but more weight on the front wheel also often helps with stability, so I can't really say. Conversely, raising the forks in the triples (pulling them up) decreases front ride height and therefore rake/trail. It typically makes a bike twitchier.