Folks - remember the OP is a newbie, so I suggest sticking to really obvious, basic differences in the first instance.
Would a pilsner malt be best for a base or should I do something else to really highlight the differences? I would prefer < 6% ABV for sure if possible.
I get where you're going with that, going for the "cleanest" possible malt background - but at the same time you've got to drink 10 gallons of this stuff and personally I would find that a bit challenging, so I would personally go for just standard pale malt.
Almost every batch I do is split 3-4 ways with different yeast, being in the UK my standard recipe is 14 or 18 litres of ~1.045 OG wort made with 100% Maris Otter, around 30IBU of bittering and then a 100g pack of hops (our standard size) smeared over 10min/flameout/whirlpool/dryhop. I guess 8oz in 10 USgal works out about the same - it's convenient to use up entire packs of hops rather than having odd bits in open packets leftover. If you're using fairly high alpha hops then you can use the same hop for bittering at 60 minutes - the odd ounce or two less of aroma additions isn't going to make so much difference, and it makes inventory even easier.
Or if you want a more neutral background, use British hops (eg Goldings or Challenger) or typical lager hops (European noble hops like Tettnang or Saaz, or US equivalents like Mt Hood or Liberty) at a lower level - say a 4oz pack split between 5 min and whirlpool.
Only comparing two at a time is a bit restricting, but if you use a similar grist and hopping and bottle some samples, you can compare them with subsequent batches.
Should I adjust the temps too, or should I leave both at the same temp?
In general, try and keep everything the same to start with, but as others have said, temperature is another parameter you can play with in later comparisons. Hefe yeast are really good for showing off the effect of fermenting at different temps.
I'm very new to brewing so I don't really know enough to know which yeasts would stand out.
At this stage you just want to get a feel for differences in the "big" parameters :
Attenuation - some yeast chew up lots of different types of carbohydrates, others have a more limited repertoire. The latter are described as having low attenuation and produce less alcohol, but leave more sugar in the beer for a slightly sweeter taste and bigger mouthfeel. Some saison etc yeast are diastatic, which means they chew up even more carbohydrates for an even drier finish - but as contaminants they can cause problems with bottle bombs etc so probably best to stay away from them in the early days whilst you're still learning to clean properly!
Phenolics - some yeasts have a POF gene cassette which converts relatively flavourless phenolic compounds into the classic "Belgian"/hefe spice flavours of clove, black pepper etc. It's the first thing most people thing of as a flavour contributed by yeast.
Esters and other yeast flavours - some yeast are more fruity etc, others are "cleaner". Different strokes for different folks.
Biotransformation - some yeast have enzymes that modify hop compounds into different flavours.
There's no need to use liquid yeast for your early experiments, dried yeast is fine, it's cheaper and easier to work with when you're inexperienced.
In general a good benchmark is a yeast from the Chico family that originated (sort of) at Sierra Nevada - so Fermentis US-05, Lallemand BRY-97 etc. They're clean, attenuate pretty well, and leave the hops alone to give a nice bright expression of the hops.
So if it were me, I think my first experiment would be :
US-05 versus Fermentis T-58 with 8oz of Chinook hops. T-58 is a bit of an oddity, it's a Belgian yeast with weak black pepper phenolics and fairly low attenuation. But it really biotransforms the grapefruit of Chinook into a slightly more muted but more complex mix that's led by lime, you would think it's a completely different hop.
Following that, I would do either :
US-05 versus a hefe yeast like Lallemand Munich Classic or Fermentis W-68 (with the 4oz more neutral hop package above) to really feel the difference phenolics can make. 50:50 wheat malt

ilsner malt to take the grist into hefe territory, or just leave it as all-barley.
Or :
Windsor versus Nottingham - representative of the two completely different yeast strains you often find in British multistrains. Windsor is low attenuation, powdery, but more flavourful; Nottingham is more neutral but has good attenuation and sticks like a rock. Be classic and use Goldings or Challenger, why not use 8oz as they're cheap.
Or use Lallemand Verdant for a British yeast (descended from London Ale III) that is very biotransformative with hazies made with Citra etc, and has a prominent vanilla note.