I think I read somewhere that the deco unit had to be before any switch?

However the subject Deco unit is only 2.5GB in and 2x 1GB out.

If I upgrade my service from 1GB to 2.5GB, is there any firm reason I can't put the switch first? 

The equipment I really care about is Hardwired LAN with 2.5GB ports installed.

My Wi-Fi performance is fine as is.

Update - I now understand that switch before the XP Pro"e" Router woulkd be a bad thing to do for security.

I have questions aboutreplacing the router with a a Deco BE 63 or BE 25 that bI will put in a different thread.