I'm getting a full gbit line and well wanted to buy a 2558 board but it seems to be getting EOL.

Here in Germany the C2358, C2558 and the C2758 are all to get the hands on! From where you are (country)?

so speed 1000/1000 over PPPOE.

Then go with an Intel Core 2 Duo or Intel Core i3, i5, i7 (embedded) or Xeon E3 CPU that is
handling that speed with eases and more on top.

at least 2 intel ports
minimally 100mbit VPN preferably higher.
packages like snort and squid.

Then a qaud core CPU or SoC might be the better option for you! It might be better
for all together I mean the 1 GBit/s, the Squid and Snort on top.

now I have 2 roads I can walk
1 is
Celeron G4400 with a Gigabyte GA-Z170N-WIFI board

You are prisoner of your own mind, you have more options then that, but often not in the same
price range like the named by yours. This one might be to low or not string enough.

The other is Supermicro X10SDV-4C-TLN4F Xeon D1518
The difference is that the 1st option is 3x cheaper.

This board is able to get here in Germany for ~597 € + shipping fee

ASUS Q87T ~150 €
2 x 4 GB RAM ~60 €
1 x mSATA 120 Gb ~80 €
Intel i350-T2 ~120 €
mini-ITX case ~60 € or
1U case + PSU ~130 €
1 x Intel Core i3 @3,0GHz ~200 €
All in all nearly ~800 € and able to serve your network as you need and wish it.