sounds very nice. dont need to tell you to watch the up stream speed for VOIP then.
Your shopping list looks fine to me for the telephone systems.
the tda 30 is the same as the 100 except smaller max 12 co and 20 digital( 40 digital if you use dxdp) and 4 slts,( in this country anyway)

when setting up the gateway, set the office and the house to different ext number ranges i.e office 101-112 and house 201-212 for the routing table

“I have not failed. I've just found 10,000 ways that won't work.”