I've reused fixer for months, nearly a year. It tends to be more stable than developer, and it's not like you have to fix for a certain time. Also, I can't ever recall measuring fixer with any more accurate than my eye. With rapid fixer, you leave the film in for two minutes, then you can check to see, in normal light, whether it's completely clear. So exact dilution doesn't matter that much, because time doesn't matter that much. It's a "when it's done" process.
For devs, using excellent D-76 (if you're starting of with BW developing, start with that or Ilford's equivalent, ID-11) I normally just throw it out after each use. D-76 isn't that expensive. Also, diluting it 1:1 (or 1+1, as Ilford lists dilutions - one part water, one part D-76 solution) gives pretty much the same results while using half as much developer. Of course, with any other developer, all bets are off as to the results.
But that's the beauty and fun of DIY BW film development. BW Devs have massive effects on the final image - some give greater shadow detail, some smoother highlights, some give finer grain, others give greater acutance ("sharpness,") some smooth out midtones, etc, etc...and all those effects also depend on what film you use. Note that fixers don't really have any visual effect.
I learned, some would say not very well, from
Kodak's Tech Pubs. ("Tech Pub" being short for "Technical Publication," of course, not a bar where geeks hang out.)
Before you buy anything, start there. They're free, and tell you only the mechanics of developing film, and, more importantly, deal with 35mm, 120 and sheet film.
A lot of other publications tend to be written by Zonies who find the idea of developing several frames of film at a time (eg, 35mm) repugnant and alien, and instead basically tell you the only way to do it is to just shoot several hundred dollars' worth of test frames, and waste them in the darkroom in order to find out the correct dev times for each single type of shot. It's makes film developing seem daunting, dull, and anal.