It depends on your play style. Sometimes people use 2 trait armor rather than 8-9 trait one. The number actually is not that important play style is. For magnb people usually use julianos light divines, kena shoulder and torugs pact swords. But you have like a million combination that you can make so check the net and combine it with your play style. Its always good to have 9 trait or friend that can do them.

Ya, basically a crafter who has only researched 2 traits can only craft certain sets. Once said crafter has reached 5, they can craft more, and sometimes better sets. This continues until they have researched all 9 traits, then they can make all craft-able sets.

For pve Magic nightblade you'll want 5 Julianos and willpower jewelry. You'll have 3 armor slots remaining if using staves, which you can do a few things with. If recommend a monster set like Kena or nerieneth of you have them, otherwise go for a 3 piece set bonus that has spell damage. Torugs pact has a 2 piece spell damages bonus and its craft able and the 3 piece bonus gives health which isn't useful for damage but it's good for staying alive if you don't have undaunted passives.
Be sure of what you want as mats are expensive. You'll have some flexibility in your build but to do good pve damage I'd recommend Eeiter 5 twice born star or 5 Julianos. And don't listen to pvp players. To be truly optimal, you should go 5 light armor with 1 medium and 1 heavy because of undaunted mettle which gives stat bonuses for armor types. If you want to be competitive you should get this passive if you don't have it. As far as how you go about getting 5-1-1, it depends on if you have monster sets or not kind of. For your heavy piece you'll want it to generally be head chest or legs. If you don't want to run a monster set then I would craft a heavy chest and medium legs as part of your julianos or main 5 piece because it's not likely that you'll swap those pieces out and makes it easy. But if you have a heavy divines Kena helm and a light Kena shoulder then you'll want to run a medium chest or legs. Kind of hard to explain and having 7 light isn't terrible.
Now for your gear you should supply the ancestor silk, rubedo, ruby ash etc. to the crafter as well as the elegant lining and blue upgrade material or expect to pay crafter a lot more. Do not have crafter make you anything less than purple gear because if you can't craft you will not be able to upgrade it. I also suggest getting at least your main bar weapon gold quality. It's not likely that you'll haves these upgrade materials and regular mats if you don't craft so look on the guild trader for them. For pve you pretty much will want 7 divines pieces so you'll need 7 sapphire trait stoned and then you'll need to decide what style you want it and provide style stones, like daedra hearts for daedric style or palladium for ancient elf.
The last and probably one of the most important part of having good gear is enchantments. Save kudas and farm as many runestones as you can so you don't have to buy them. Legendary enchantments make a huge difference in the amount of damage you do and give you a larger stat pool. I personally neglected doing this for a long time and you'll do just fine with regular enchants but eventually once you're set on your build, Golding out everything will get every last bit of performance out of it.
As for a tip, I wouldn't do less than 10k and if you're getting multiple crafted sets then I'd do more but I always craft my own and have never been in this situation. Just be generous if they are doing a lot for you but also come prepared and do your research on market value of mats if you don't provide them.
And lastly I'd recommend becoming a crafter. It's so convenient. Getting to 50 in a trade doesn't take much and researching traits actually comes fairly quickly if you're actively on top of it. It's only when you get to 8 or 9 traits when it gets annoying and same thing with motif farming as a lot of the new motifs are expensive or very tediously obtained. But honestly it's just difficult not being able to craft. Even if you don't research anything or craft anything at all you still gain a lot by having the skill line maxed out ( better deconstruction yields, not having to buy mats because you'll see them instead of jute.)
Anyways good luck and don't get ripped off or treat your crafter poorly