If you can afford to do so, replace ALL the flooring with on-site finished oak flooring. DO NOT use a dark stain - it shows dust and just is impossible to keep looking good. Choose either a light color or a mid-range color (I prefer the mid-range). You'll be glad you did this and it will increase the value of your home.

Most tack strip comes with hardened nails (check before you buy) but they do require a bit of skill to drive into concrete. Basically you want to drive them with one clean strike which typically requires heavier hammer, a fast arm, and a good eye. Tapcons are a brand of concrete screw, synonymous with the category like Kleenex is to facial tissue. You don’t need any kind of special epoxy to use them. Basically you drill a pilot hole with a masonry drill bit and then drive the screw. A hammer drill will make drilling the pilot hole a lot easier but it’s not absolutely required. You could also use ordinary screws and a plastic anchor just like you would with drywall. Another option (and a lot of fun) is to use a powder actuated faster and I suspect what the original contractor may have used (although there are pneumatic concrete nailers as well). Hilti and Ramset are two brands associated with the devices. Basically they use a .22 blank cartridge to drive a nail. A bit of a learning curve, modest investment ($35 for the tool), eye and ear protection absolutely required.

Find your budget for the whole thing. And then work backwards. Example...if you have $5000 for budget and you have 1500sf to cover, that means your budget is $3.33/sf. Carpet and pad are sold separately and by the square YARD (3ft x 3ft = 9sf). If your budget is $3.33/sf...that means you have $30/square yard. Now you pick your carpet (by the square yard) and your pad (go with the highest level pad you can afford that is allowed with the carpet). Add the two together to get a "per Square yard" price. A well established CARPET STORE will offer 'installed price'. Work with that number. You have to leave room in your budget for installation costs.

If the chevron was a good color I don't think that would be a bad choice. It might look busy to you because it's different than what you have now, but perfectly acceptable for stairs. I bought carpet not too long ago and it seems like tweady colors are popular - two or more different colors mixed (in a subtle way - really just different shades of the same color). You might have better luck with something like that instead of a solid. Bring home as many sample boards as they will let you take at a time and broaden your scope to include things that are different, like the chevron pattern.