Once you find a daily vape, then a nickel per mil is about normal, much cheaper than juice. The problem, though, is that you can spend hundreds getting setup and on flavors that won't taste just right, as you mentioned.
I've only been doing DIY for about 10 months and I have to say that I couldn't make anything very good for about the first six months, yet now consider myself pretty good at it. What happened? What made the difference?
1. First, I discovered what I liked....pastry, fruits and sweets
2. Some things that taste good, don't translate into good vapes (for every rule, though, there are exceptions)
3. For example, live for chocolate. Not easy to make a good vapeable chocolate (but nothing is impossible)
4. Get a good DIY calculator like Ejuicemeup.
5. Go to the DIY section. Select a preferred flavor maker, like Flavor Art, Capella, The Flavor Apprentice, etc.
6. Find threads on the vendor you selected and look through the threads for starting percentages. For example, use cherry at 1%, or peach at 10%. This will save you gallons down the line. Because of steeping times, it's hard to make twenty 3-ml batches of a flavor to discover the starting percentages yourself. It literally takes forever.
7. Some flavors don't play nice with others, so complexes mixes need to come after single ingredient mixes (at first).
8. On those same threads where you find the starting percentages of TFA (the Flavor Apprentice), for example, there will be hundreds of posts from experienced DIY'ers sharing their recipes. These recipes will usually taste much better than anything you can make at first. Give them a try.
9. A little of this, a lot of that....hardest part to learn. Trial and error for me, plus following a lot of recipes by others. Some flavorings are super strong at 1%, others not that strong at 20%. Takes time, a lot of trial and error to learn about these "pinches of salt."
10. A one-flavor ingredient can be ready to vape in two or three days. A two or three flavor recipe in 5 or 10 days, complex recipes with 8 or more ingredients can take 5 weeks to fully steep. Flavor bonds take time to form., The more flavor bonds that need to form, the longer it takes.
11. Subtle flavors may be undetectable for days or weeks, and then just show up down the road. Some stronger flavors, like an eggnog/nutmeg, can seem to overpower everything else at first, and then fade to the nicest subtlety, over time.
12. Many juices will undergo several, say three on average, distinct flavor changes over the first 4 to 6 weeks. Be patient.
13. Make small test batches, say 3-4 milliliters at first.
14. You cannot have too many bottles, too many sizes, too many syringes, too many beakers, too many pipettes, or too many flavors.
15. Buy in bulk where possible. These bases and nicotine bases are inexpensive in larger quantities. I usually buy nicotine by the liter or more, to keep the cost down, while preparing for the VapAcalypse. I usually buy my flavorings in 4 oz bottles for my ADV's, at least 16 oz for the PG and VG bases, 1 oz for most flavorings, etc. So, it is expensive up front, not less, but way cheaper down the line. I have enough juice, bases and nicotine to last about 3 years. I freeze the nicotine that I don't plan to use in the next year...to answer one of your questions.
16. Get ahead of your juice requirements. In other words, make juice for next month, now, so everything is fully steeped when you need it. One of my juices takes a solid 5 weeks to steep, undergoes three distinct flavor changes, and ends up as an ADV for my daughter. I'm 5 weeks ahead at all times on that juice.
17. Don't throw out your early experiments. Sometimes they come back to life and are amazing.
18. Keep meticulous records. I keep my recipes on my calculator, have a backup file and a hard copy paper notebook. I use a Brother P-Touch to label my juices using 3 lines of type on each label. You never know when you're going to make something great, and you sure need to be able to lay your hands on the recipe again. I heard about a guy who DIY'd some juice, discovered it in his glove compartments six months later, that was to "die for." Unfortunately, he no longer had the recipe.
19. The mad scientist thing is important at first as your learning to make the juice, precision, etc. However, after a while, you can slap these recipes together before coffee has time to brew. They can be off by a bit of this or that and still nearly identical in vape, as long as you're pretty close.
20. Be very careful with the nicotine. Start with amounts no higher than probably 36 mg/ml. When you are comfortable with mad scientist in you, up it to 60. After a longer time, more care, etc., I buy only at 100 mg/ml and dilute to each batch. Since this 10% nicotine solution is in a 90% base, it's not deadly if you get some on you, but don't linger getting it washed off. Always use gloves and eye protection. Even if you get a drop on you, you will begin to feel a burning sensation pretty quick, so use safety precautions, start at lower levels, work up from there, always use care, avoid distractions, pay attention, and be patient.
21. DIY is every bit as much fun at any other part of vaping, maybe more so. I have taken months sometimes trying to get a single recipe just right, and when you do get there, there's a great sense of satisfaction, just like you would have in any other endeavor and accomplishment. Always remember, safety first.
MOST IMPORTANTLY: BE PATIENT. A large investment into the DIY is the only reason I still DIY, as I could not walk away from my investment, and just had to doggedly keep up at it. A few months ago, it finally clicked, and now I make pretty tasty juice, or so I'm told. I don't think I've actually tasted anything since 1975, so I can't be sure, but others give me a thumbs up, and I share recipes with friends here on ECF that confirm this. Nothing to this other than if I still suck at making juice, I need to know it, is all.
I have 6 ADV's today. I have made several hundred different juices. I make about 20 good ones now. Considering that six months ago I made one ADV and one other good one, I've come a long way, and no one was more surprised than me, when the DIY fairies finally green lighted me to enter the inner sanctum....TG. I doubt I've saved anything yet, but over the next three years, I estimate that my next 15,000 - 20,000 mils will be close to free me and the family. I doesn't get much better than DIY, because you can learn to make it the way you like it, and no vendor can ever beat that. It's the best part! Good luck, power up and vape on!!