Dextrose is not going to work well. It has(is) sugar, but lacks other nutrients needed for yeast health. Just buy some DME if you don't have it sitting around
Don't try to rinse out the yeast. It's a huge risk at that stage to no benefit. Just don't worry about whatever is left in the bottle. Schwirl it up, get as much as you can in one swift clean pour, and relax.
As far as sugar ratios yadda yadda, you're overcomplicating it. Just get some DME, make a quart of half gallon of "amber" wort, pitch your yeast in that, and go. It's not a big deal, and a wide range of strengths work fine. Remember, you're just trying to increase the yeast population and vigor. So type of beer and all that really doesn't matter.
Don't overcomplicate it. It's really very simple. But do use DME or you won't like the results. Cheers