The main reason for not using the same fixer for paper and film is not concentration, but silver build-up. Film can tolerate a MUCH higher silver concentration than paper, at least FB paper -- I've never thought about this question in relation to RC. This is why, if you use film-strength fixer for paper (as I and many others do) fixing is much faster but the fixer capacity (area/litre) remains the same.
I disagree STRONGLY with Ruben's 'biggest recommendation', though. At first, try as many films and devs as you can. Some have a 'magic', others don't, and what is really strange is that what works for one photographer won't for another: pure alchemy.
If you don't want to spend a fortune on devs, buy just one and try a wide range of films in it. There are however major differences between devs. This is why there is no longer a standard ISO developer: manufacturers can determine ISO with any developer, as long as they say what it is.
Some devs give a true ISO speed increase (more speed with no extra contrast): Ilford's Microphen and DDX and Paterson's FX50 are good examples, and give ISO 650 or even a fraction better with HP5 (nominal IS0 400). The penalty is bigger grain.
Others give finer grain but less speed and lower sharpness (the latter is counter-intuitive, but true), or higher sharpness but slightly coarser grain, etc. Some sell on tonality alone: many (though not I) love the tonality of Rodinal but it gives low speed and big grain with many, perhaps most, films. This is why there's a whole module on developer choice in the Photo School
www.rogerandfrances.com
Even 'bulletproof' combinations like Ilford HP5 Plus in Perceptol (true ISO about 250) won't work for everyone and if you choose the wrong film/dev combination you can waste all of the two years Ruben advocates merely trying to make the chosen combination work satisfactority.
As soon as you find a combination that gives you the 'magic', yes, I'll second Ruben. But until then I think it's dangerous advice.
Cheers,
Roger