So Rollei RHS seems not to be the best point to start at. Xtol is a very good choice as a standard developer, but only fully economic when you develop about 50 films per year because unfortunately it is only available as a 5 L pack in which at least 50 films can be developed. Xtol is powder, you have to solute it in water before use. It is very cheap per film, so if you not use it completely before it gets bad then there is no big waste of money. If Xtol is not comfortable for you, then start with an oldie but goldie - Kodak D-76 (Ilford ID-11 is the same).
Originally Posted by AgX
The choice of the fixer is uncritical. And as a stop bath water does the job, if changed three times or you take wather with some vinegar from your food store added.
Good luck then, developing is fun,
Xtol is a good choice, get yourself some smaller bottles, 250 or 500 ml, and fill to the top and store until needed. Then use one shot or 1 to 1 as needed.
D76 or ID11 is another to consider.
AM74/RHS is a very good developer to start. It's a semi compensating Phenidone/Hydroquinon developer, pH around 10. With a lot of films a perfect result. 1+7 (possible as stock) but preferable 1+9 till 1+19 as one shot. The minimum amount of developer is 20ml / each 135-36/120 roll film.
Only Tri-X (400) and HP5+ in 35mm are not recommended due to the bigger grain (compared in D76 equivalent). It's also noted in the manufacturer recommendation.
Still very populair in BeNeLux and Germany: