Nearing the end of my questionable career in monstrous regiment (guild) I had picked up fishing and trained cooking in tandem (something that is easily done although does result in a bit of travel around the world).
I am not going to recommend any specific guides to train fishing and cooking at the same time since there are a ton out there and I really just fudged around with it myself till it was what it is now.
Google it if you're interested I am sure you will find a ton of advice.
The big question however for me was always: Why should I pick up fishing and cooking in the first place?
The answer is obvious if you're heavily invested into raiding. Stacks of buff-foods can cost a pretty penny and if you're going raiding more than once a week you're actually burning gold purely on consumables which you are not likely to get back during your raids.
You could opt to raid without consumables but a lot of guilds will frown upon this practice.
But what if I don't raid?
Then you are most likely in the position I am in now. Guildless, doing 5-mans and generally having a good time levelling some alts. Buff foods can be helpful sometimes but they're not needed and definitely not worth buying.
So why fish? Well, fishing is pure gold. At lower levels firefin snappers and oily blackmouth as well as stonescale eels and deviate fish are in decent demand with alchemists and crazy people. At higher levels you can practically turn any fish into some useful buff food which will sell for quite some gold on the auction house.
With profits ranging from 5g for 5 deviate delights to 30g for a stack of fisherman's feast it turns out that there are very little things you can fish up that are worthless.
All the extra things you fish up out of pools of fish like crates, 'junk' and motes of water are generally gravy and can usually also be sold for a decent profit (even junk seems to be valued quite high).
In terms of value for money it is very much possible to get the same, if not more money from straight up fishing than you can get doing dailies because you can just stand and fish rather than having to whizz all over the place to get dailies done.
Combining dailies and fishing is without a doubt a good idea and can generally be combined fairly well (considering the fishing and cooking dailies send you places where other dailies can be done).
All in all it's good not to underestimate fishing as a source of income and the time invested is usually not as big an issue as people make it out to be simply because you make money as you train.
In wow, fishing truly is catching and there is no cost involved.