Test with 3/4 cup of the base and 1/4 cup of the white. At best, it will seal the old picket fence before you use the white paint. At worst, the two brands will react badly and refuse to dry or peel off in a few days. Mixing brands of paint does not always work - they might have incompatible ingredients and curdle. You can get 5 gallons of Valspar white exterior paint for about $80 ... maybe 2 coats of that for about $160 would be better than this messing around with odd mixtures that might noit work.

Can you take a straight on shot of the foyer so we can better see the area rug placement? From looking at the floor on the sides of the walls it looks like it's off center. That would bug me. I think I'd prefer a long runner. How wide is the entrance/hall? Maybe a small area rug at the door and then a runner. Very pretty house! I'd leave your console with mirror as is. It looks nice. I really like the bench but that's a long wall. I like the above suggestions. I also wondered about doing three related groupings. Something right over the bench and one on each side. Whatever you do with art I think large. I think the photos and diploma frames are too small. If you want to use them I'd get larger frames and mat them. Are they 8x10s? At least 11x14s and you can easily find mats and frames inexpensively for that size. ETA- Looking again, it looks like the bench is centered on that wall and the area rug intrudes into it's space. I think we need to see a different view of the foyer area but I think (hard to tell) if you keep the rug the bench would look better moved down more to the left. With art then above it it would be anchored and look intentional event though it's not centered on the wall. I had to do this with my foyer. The buffet I have is moved down because of the door so the mirror and buffet aren't centered but it doesn't look weird if that makes sense. Also, could you put the front feet of the console over the area rug so that it's centered? Again, hard to tell. These suggestions may not work but things to consider/try!

I’m not a designer but I think your instincts are right. If everything else is super light I agree the sofa will look too dark and heavy. I think a light, warm neutral paint would be great, and accents of blue would make that gold sofa sing. I think your existing neutral walls look okay, actually. What if you just tried painting the red accent wall a nice mid tone blue?

The yard does not have to look like a recycle salvage- the cheap/recycled pots can be camouflaged with the much nicer wood planters just like garden nursery pots. In the case of using the square storage bins or kitty litter buckets, they fit/fill a bit nicer into a square wooden box surround than round pots can. Garbage cans don't have to look garbage either- there are attractive ones out there. Or at least ones that more decorative or meant to be seen and look like pots and don't necessarily need to be hidden. They can also be handy for container growing stuff with deep roots. I container grow horseradish and salsify, and just couldn't find any pots that were big and deep enough till I found a nice trio of plain round heavy plastic garbage cans- they look a lot like the big pot on the left in the OP pic, only they came in black.