As you know, there are between one and four boxes; combined wireless modem-router all-in-one, or 1. modem + 2. firewall-router + 3. switch + 4. wireless access point(s). The more boxes the better the performance. If you want excellent wireless coverage you might have more than one wireless access point parked in suitable places that are best for coverage rather than being dictated by where the dsl line comes into the house. I have more than three boxes in fact (two wireless access points). If you have a lot of wired devices then a separate LAN switch will be needed rather than the very small ones that are provided in some firewall-routers.
Many of our members are fond of ZyXEL modems, there are various opinions as to favourites for firewall routers, switches and wireless access points.
I use ZyXEL VMG 1312-B10A modems, a Firebrick firewall-router, an HP switch and two ZyXEL wireless access points. Those particular modems are not being manufactured any more but can still be found on eBay; a better option would be to ask about other current top if the range ZyXEL modems. Some ZyXEL modems are notably better than others, so definitely ask. The ZyXEL xxxxx-B10D is an inferior device so watch out. My ZyXEL wireless access points are really really old but they have a rich feature set. My Firebrick FB2900 firewall-router is expensive but I love it.
Sorry that’s not more helpful. I’m home others will chip in with suggestions.