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I'm struggling with where to begin.
The gun in question is a Howa M1500 in .223 Rem with a 1:9 twist
Start with the bullet. Twist rate and barrel length will limit how heavy a bullet you can use (stabilize). Bullet weight and ballistic coefficient are two major factors in effective distance. For your 1:9 I wouldn't go above 69gr EXCEPT the Hornady 75gr which shoots amazing all around for that twist rate.
For shorter distances (100 yards) you'll want a lighter flat base bullet. 50-55 grain bullets shoot great at these distances. My favorite is the 50gr Horandy Z-max. For lighter bullets use a faster powder like Benchmark or H335 as mentioned above.
For 300yards+, you'll be maxing out your twist. 69gr SMK should shoot well or the Hornady 75gr. Choose a slower burn rate powders for these bullets like Varget, H4895, N135, N140, RE15, CFE223, AA2230... just depends on what you can get. Extrude powders like Varget and H4895 are more temperate stable and won't need adjusting based in the seasons. Spherical powders such as AA2230 or CFE223 will meter better (particularly from powder drops). CFE223 and RE15 tend to have more carbon fowling that some of the others.
If your hunting, you'll want a bullet specifically designed for optimal expansion. For varmint hunting the 50gr Z-Max should work well (I've never actually tested this).
Your optimal cartridge over all length (C.O.A.L.) will be determined by the type of bullet your using. Elongated bullets (tangent) such as VLD bullets prefer to be "jammed" into the lands. Stubby (secant) bullets like to be "jumped" into the lands.
Since you're just starting off, stick to the recommended book values for overall length. These tend to be magazine length values. FYI, the Hornady 75gr and Z-max shoot well jumped.
A good starting point for optimizing jump of secant bullets is 0.025" from the lands. A Sinclair overall length gauge is the best way I've found to measure your distance to the lands. Take care when optimizing length as pressure can spike rapidly as you approach the lands.
VLD bullets, such as the Berger VLD or Hornady A-max, require C.O.A.L. tuning to get them to shoot the best. They like anywhere from 0.005" jump (off the lands) to 0.010" jam (into the lands). Or they might even like to be jumped.
For primer types, just stick to what you can find. Federal GMM, CCI BR4, Wolf/Tula and Winchester 7 1/2 are all good options. Sometimes people have problems piercing primer cups and need a thicker cup, mostly in semi-auto guns. FGMM and wolf non-magnum primers tend to be thinner. My go to primes are Tula and BR4 primers.
When I started loading my friend told me "it takes a while to be able to make accurate ammo, for now just focus on just my blowing up your gun". Never a truer statement could be made.
For load development, make sure you're keeping a journal or log. Record your component types, COAL and lot numbers. You'll being kicking yourself in the ass if you forget your load data. I recommend reading Eric Cortina's 1000 yard development at 100 yards thread. Also, Google OCW load development.
Your book values will determine your starting and maximum loads. Always start with 10% below your max load. Software such as Quickload can be used in lieu of manuals and when used correctly can help you find the true maximum load / accuracy node. I work up in 0.5gr loads which allows me to easily see the amount of "group vertical offset". The ideal charge weight (accuracy nodes) will have the least amount of vertical change between its neighboring charges.
I shoot 3 or 5 shot groups depending on how bad the weather is. I use 1 MOA dots or a Sinclair practice target. To measure my groups i use OnTarget. I put all my data into an excel file and then plot the verticals offsets into a chart. Assuming minimal shooter error Accuracy nodes will be blatantly clear by looking at the target.
If you're unsure which charge weight is the best, post your target picture here and people will help you out.
Or am I misreading you?
