Having gone from factory rifles (Tikkas) to customs, I would say there is some wisdom to going custom early on - if you have the support you need if things don't go as smoothly as one always hopes. I personally wouldn't go full custom without having a good local smith to lean on.
If you want to believe you can buy used parts and screw them together for your first precision rifle and be guided by the wisdom of the internet, you are the definition of optimism. Or some other word. If you've built ARs, that's something.
In addition to the pieces and basic tools, you'll need a barrel vise, action wrench, torque wrench, and go/no-go gauges, and the knowledge to use them. The internet knows all. Hopefully you have some local expertise to get you started.
If you get everything together and there's an issue - pieces don't fit, gun won't shoot, whatever - are you comfortable that you can get the help you need locally? If not, are you good with sending your rig off... someplace... for troubleshooting, paying for it, and doing without the firearm for however long?
Of course, there's no guarantee that a factory rifle won't give you trouble. One of mine suffered a primer light-strike issue, wouldn't reliably fire CCI 450 primers. LGS where I bought it sent it back (on their dime) to Beretta, where it sat for five weeks, and was no better when I got it back. My longtime friend and gunsmith diagnosed and fixed the issue - improperly radiused firing pin tip - in 15 minutes.
I just put together a custom on a Defiance Deviant w/ 2 bolts, Trigger Tech Diamond trigger ,and Bartlein barrels (.223, 6.5CM) in an MDT ACC chassis. Not an "entry level" rig. The 6.5CM runs as slick as my TAC A1 did, and that's saying something. The .223 - almost. Cartridge sometimes hangs when almost fully into the chamber. Once again, my friend & gunsmith, who did the barrel machining, diagnosed the issue in minutes and will do the moments of lathe work to fix it as soon as I'm ready to give it back to him for a day or two. Oh, and we all learned from Defiance that you can put a .384-face (for .223 Rem) bolt in a Deviant action originally shipped with a .473 bolt face (for .308, 6.5CM, etc), but not the other way around - the actions are not the same.
If a hiccup like these happened with your new rig, can you get help locally?
Did I ever feel like I made a mistake buying either of my Tikkas? No.
Did I ever regret not going custom first time around? No.
Is my new $3300 custom wearing a $3600 scope more accurate than my $1700 Tikka wearing a $1600 scope? Not over $3500 worth.
Does it make me more competitive? O gawd no.
Do I feel more accepted by the cool kids because I'm not shooting a factory rifle anymore? I have no idea, and the reality is I do not give a single flying damn about the opinions of dipshit pricks to whom such things are important. I've had the honor of shooting with a few legends in their disciplines, and not a one of them ever acted like that kind of asshole.
If you can get a TAC A1 in 6.5CM with a 24" barrel for $1600, you'll get an excellent rifle, and I'm pretty sure Beretta is still doing the free third magazine offer. Yes, it comes with a flat rib. But any decent scope will still get you to over 1000 yards. Yes, the Tikka barrels run a little slow compared to most others - but barrels are consumables. If you go custom, that's great too. Just make sure you go in prepared for unexpected bumps in the road.
