It really depends upon your playstyle. Just remember one major point - perk whatever skills you use, and use whatever skills you've perked. If you just want to dabble in alchemy or enchanting, one point in either is all you need. That 20% bonus for the first point is a huge improvement. The one thing to remember is that it is very very very easy to level yourself up with either of those skills, and if you don't use what you've made with them, you can find the enemies are tougher than you can handle with your primary magic skills.
Yep I had that problem. I reached level 40 without spending any points in any trees except smithing, enchanting and alchemy, and combat was quite difficult at times. My level was way higher than my actual combat skill. I used conjuring to help me defeat the tougher enemies and so that also reached 100.
However, once I reached 100 in all three and finally smithed, improved and enchanted my gear, combat became laughably easy. With my dead thralls, their upgraded gear and my follower there's nothing I can't do. I can wipe out entire towns without doing anything. Literally. I can stand there and my thralls and follower kill everything in sight.
I got 100 skill level in alchemy, enchanting, and smithing. It took a lot of repetitive work except for alchemy. I also got 5/5 in enchanting and alchemy perks. I did not make overly powerful potions for enchanting and smithing. I only made basic potions for those. Even so, this has made melee combat a little too easy. Also I don't care about the special weapons and armor from dungeons anymore, since I can make better weapons and armor. However I still get killed easily from fire attacks by dragons because I haven't made any apparel to protect me from fire.
My advice is DON'T put a lot of extra effort, time, and perks into upgrading your enchanting, alchemy, and smithing as fast as possible. It kind of spoils the game.
Just play normally and let these things build up at a normal and natural rate of progression.
I recommend you just make yourself powerful enough to the point where you just don't get your ass kicked too easily and be humiliated frequently in battles. You want the game to still be challenging.
Exactly. If you aren't careful it can spoil the game. You have to actually plan how much of a bonus you want so that the game doesn't become too easy, and even then a lot of the "magic" is gone. You won't care when you find a particularly nice weapon or armor because it will pale in comparison to what you can make. You won't care about encountering a tough boss because
nothing is tough. Dragons become a serious nuisance because they pose no challenge and lose all sense of epicness. Pair that with 100 conjuring like I did and the entire game becomes a cakewalk. It's like playing with god mode on.