I played the game heavily from the late 2000's to early 2010's before taking a decade long break and recently got back into it. What I'm getting at is I'm not an expert or much of a veteran. Regardless...

Prepare for an addiction, my child:

1. archive.org's legal ISO: https://archive.org/details/ut-goty
   
2. ut99.org's official "it's free" post (plus installer links): https://ut99.org/ut99.org/viewtopic.php?t=16618

tl;dr: Don't forget to do some online searchin' for Renderers, HD textures, utilities, map packs, and gametypes. There are a number of (optional) posts explaining how to get fully started with (and tweak) the game, btw. Just gotta search 'em up (here's GamingWithSilvertail's from January of 2021). Whether or not every suggestion in such guides should still be followed after OldUnreal's v469c[github.com] patch in October is a different matter that others can comment on.

• Unreal, Unreal Tournament free on Internet Archive[www.polygon.com]
  
• Classic Unreal Tournament and Unreal now easier to download free thanks to OldUnreal (updated)[www.gamingonlinux.com]
  
• Classic shooters Unreal and Unreal Tournament are now free and preserved on the Internet Archive

Just install v469d[github.com] (or the latest official release[github.com]) and enjoy the game. Excluding Key Sites, everything below is the absolute most I'd recommend a new player to dive into. The game's got a very long mod history afterall.

• JaFO's Bot-editor v2.5[medor.no-ip.org] (highly recommended unless using XBots9b)
  
• UT Map Manager v1.5[ut99.org] (download[ut-files.com]) (install/uninstall zipped maps and umods, install cached maps)

Options for handling umod files:

• UMOD Browser[ut99.org] (UNIX & Windows)
  
• UMOD extractor[ut99.org]
  
• UmodPack[web.archive.org] (Linux)
  
• FormatUmod[ut99.org] (aka: "7-zip plugin for open UMOD")
  
• UT99 Registry Fix[ut99.org] (to make umod files launchable on their own)

• v469d[github.com] (or the latest official release[github.com])
  
• Bonus Pack #4[unrealarchive.org] (GOTY already has #1-3)
  
• Bonus Pack 4 Fix
  
• Advanced Model Support
  
• High Definition and UltraHD packages[www.oldunreal.com] -> HD Texture Pack 3.5
  
• AssaultBonuspack418[unrealarchive.org]
  
• MonsterHunt613[github.com] (or the latest release[github.com])
  
• Hermskii's MHM Maps (55 curated Monster Hunt maps)
  
• UT-XANITY-V2's Marginally Enhanced UT version 100[web.archive.org] (highly recommended unless using XBots9b or XBots055)
  
• LoathsomesBotPack[unrealarchive.org]'s AdjustoBots (fixes Auto Adjust Skill) & XBots9b (expands limit to 320 individual bots)
  
• xbots055 (highly recommended unless using XBots9b)
  
• BotOrders[ut99.org] (automatically gives bots helpful orders after start of game)
  
• FixBots v2[ut99.org] (periodically checks & corrects bot movement, unless using SmartStockBots)
  
• FixCTFBots[ut99.org] ("Periodically check all bots and set AlternatePath when bots return flag to home base," superseded by SmartStockBots)
  
• IRoamer_03_2022[ut99.org] (better AI for InstaGib game types)
  
• MBot_F_Gen2_updated[ut99.org] (better AI for specific bot pack)
  
• FerBotz_20[ut99.org] (better AI for specific bot-like pawn pack)
  
• ChaosUT v1.1[chaoticdreams.org] (+ChaosUT Desktop, Chrek Player Model, map packs)
  
• SmartStockBots mutator[ut99.org] ("many fixes for different game types and cases")

• https://ut99.org/index.php?sid=6381d58d3380de175fe3a292375f0de5 (tons of downloads)
  
• OldUnreal[www.oldunreal.com] (downloads) (forums[www.oldunreal.com])
  
• ut-files.com (tons of downlaods)
  
• https://www.moddb.com/games/unreal-tournament (tons of downloads)
  
• https://www.unrealsp.org/viewforum.php?f=4 (lots of downloads)
  
• UnrealTextures[sites.google.com] (HD textures, HD skins, renderers)
  
• UnrealArchive.org (tons of downloads)
  
• Gamebanana[gamebanana.com] (many downloads)
  
• GameFront[www.gamefront.com] (tons of downloads)
  
• http://medor.no-ip.org/ (tons of downloads)
  
• SkinCity[skincity.beyondunreal.com] (screenshots and info for 240 different skins/skinpacks, downloads broken but still useful)

• GameTracker[www.gametracker.com]
  
• 333Networks[master.333networks.com]
  
• UBrowser[ubrowser.333networks.com] (external server browser basically)
  
• Reddit post with more active servers

https://eatsleeput.com/ has 5 active servers. Here are the two USA ones:

• --- ComboGib CTF (Grapple Hook) -- Atlanta --- 173.230.132.25:7777[www.gametracker.com]
  
• --- ComboGib DM (Grapple Hook) -- New York --- 23.92.16.218:7777[www.gametracker.com]

House of Hermskii {HOH}[www.hermskii.com] has two servers:

• Curious George's Redeemer Insanity {CG}: 75.43.140.254:7757[www.gametracker.com]
  
• Monster Hunt Mayhem {MHM}: 75.43.140.254:7737[www.gametracker.com]