Yes, there are a lot of USE flags, but this is part of the extreme flexibility gentoo's package management offers. I have tried to use other distros several times but I always wind up returning to gentoo for the package management flexibility. Remember heartbleed? All I had to do was toggle a USE flag to disable the tls heartbeat and recompile openssl immediately. It was patched eventually, of course, and it could be reenabled again. However, as far as I know, other distros had no easy way to do this, unless you had source tools and did things outside of the package management system for the distro.
There are a lot of USE flags that are shared between lots of packages and this can be enabled globally if need be (thinking of things like printing support, hardware video acceleration, etc.) There are ways to deal with USE flags.
1. First, get the base system running (no gui, just get it so you can login to a shell.)
2. Set a profile (use `eselect profile list` to show them, and `eselect profile set x to set one.)
3. Use `emerge --info` to set what flags are used.
4. Use `emerge -pnuDN world` to see which packages will be compiled. USE flags triggering the change will be highlighted.
5. If you're wondering what a specific USE flag is doing with a package, use `equery uses <package>` to check. equery is in the gentoolkit package.
If you need changes it is better to set USE flags for individual packages as someone else posted.
Yes, this takes a while to set up but once it's done you will know what you need and it can be noted somewhere.