That's like trying to learn to drive in an F1.
Get a boosted Camaro first.
for what it’s worth though, 338 LM was my first “ELR” weapon system. It was my first true stepping stone into the world of long range precision. I had very limited reloading knowledge before this too. My shooting activities before this just consisted of pinging steel at 1-200 yards with AR’s.
My advice to OP is this - abso-fucken-lutely hell yes you should do a 338 LM. Some things I’d make you aware of though: the investment doesn’t stop - ever - at just the rifle and scope. You’ll need, ballistics solution solver, rangefinder + tripod, chronograph, hand loading supplies including: press, dies (you want good dies), powder measure, collet style bullet puller, a decent pair of calipers, brass tumbler, brass trimmer, bullets, brass, powder, primers, etc. there’s a lot of other smaller reloading tools you’ll want too.
There’s a video on YouTube of this guy banana ballistics who tells you not to get a 338 lm because it’s like sending a $6 latte down range every trigger pull. Don’t listen. He’s likely a chill bro, but his message misses the mark. I can buy reloading supplies as follows:
1x fired Lapua brass: $1.70-1.90 per (gunbroker)
1,000 primers: $0.20 per for a GM215
Bullets usually $100 for 100
Powder: $0.73 ish per cartridge.
Now excluding brass cost you’re looking at under or around $2.00 per shot. Which honestly isn’t bad and I typically am not putting more than 30 rounds on the barrel in a single day. So dont let anyone tell you that this cartridge is “expensive” because trust me, my alternative is shooting triple digits as a guest at the country club for easily triple the cost.
Snipers Hide has been a great resource for me to ask questions too about hand loading. The guys in the 338 LM reloading thread are class acts and will help you get situated with your loads and once worked out these things are dead ass accurate, and they pack quite a punch.
However… realistically the cartridge is not that strong of an ELR rifle. I’m reluctant to shoot the 338 LM beyond 2,200 yds as it falls off pretty quickly there after. Thus it won’t serve you well as an ELR competition gun since they’ll have stages where you’re shooting 2,500 plus. 338XC is the minimum I’d recommend for that but 375 ct is what’s winning there. But for 1 mile, hell yah you want the 338
And to answer your other question, no. You will NOT want to shoot 338 LM for a PRS style match. lol. Not only would that be a poor choice of rifle and they probably wouldn’t like you punching holes in all their steel, but you can’t just switch the barrel from 6.5cm to 338lm. They require different actions and bolts. The AXMC can do both, but that’s a considerable step up in investment over the MPA.