This is entirely up to personal preference. If youre enjoying conj/whm and want to blaze through the story feel free. We play to have fun, so do what feels right. The extra abilities you get do make you stronger and better equipped to handle everything though. For instance, at some point pretty much all healers do end up taking a 26 level run through thaumaturge because the cross class skills that nets you are super useful(the arcanist ones arent that bad either). Surecast(next spell cant be interupted by being hit) is actually more useful for you then it is for them, and Swiftcast(next spell has no cast time) is an absolute life saver. At level 28 or so you get a trait that lets you cast raise during a fight, and being able to do so instantly(once per min) can be the difference between a close call and a party wipe. It gets more helpful the higher you are, as more and more fights will try not to let you sit still long enough to get a raise off. For parties that arent having trouble, you can be creative and weave it into your abilities in other ways(swift+stoneskin to take the edge off the bosses big attack you know is coming for instance). Some people put the cross class skills off until closer to 50 or later, others do it as soon as they think itll be useful. Thats your call to make, though you will end up using it a lot as soon as you have it. You also may enjoy burning things for awhile after healing them for so long.
And to clarify one point on crafting. Starting out isnt a money sink unless you make it one. All or almost all crafting mats up to around level 15 can be purchased fairly cheaply off vendors in the towns if you look around for them. And typically, the ingredients you use to make things are gotten at or below the level you use them, to make items roughly the same level. So for instance, around level 15 a blacksmith starts to need iron to make weapons and tools. At around level 12 miners can start getting iron ore out in the field. And the weapons that the blacksmith makes from them will be about level 15, and can be put to use(possibly getting more materials). Early crafting becomes a money sink if you end up buying all your mats from other players(instead of getting some on your own) or if you try to power-level large ranges(buying finished leve turn ins from other crafters for instance). Basically its either a money sink(buy everything, go fast) or a time sink(get some/most yourself, go more slowly), so dont feel you have to wait just because you arent rich. When youre ready(or just want a break from leveling), dip a toe and see if you like it.