The AmpliFi is just a consumer friendly brand that Ubiquiti built. https://amplifi.com/ Much like Linksys was to Cisco.
It doesn’t have all the features their edgerouters. The access interface is via a phone app(downside), but it is dead simple to setup, and generally secure with auto-updates as a feature.
for the IOT devices i would suggest making sure your router that sits between your modem and home network can setup one way internet connections so it can speak out but not receive for things like security cams. Or at a minimum make sure that you can limit what ports it can use. there is always as ASUS calles it putting devices on DMZ that you want to talk out to the web and only the web.
LastPass or some other alternative. All are technically insecure (anything over the WAN can be hacked), but easiest for you to setup, and NOT manage. Something more secure would be Keepass.
DON’T MAKE THEM AVAILABLE OVER THE INTERNET. Have you never seen this subreddit??? Also, a couple of analog security cameras (BNC jacked) will probably be good enough. Most can do 1080P for quite little money.
NO. None of this crap
A couple of Ubiquiti AP’s is probably good enough, but if you got the money, go for Meraki or Aruba stuff if you want top of the line.
If you were really security conscious, you wouldn’t use JUST the cloud. Instead, you’d setup a home NAS with some sort of RAID (raid 1, raid 6, etc), along with some long-term file storage (LTO, Archival BluRay, etc), use software to auto-backup the devices (Sweet Home, Super Backup, SyncMe, etc )and encrypt all of your data before sending it to the cloud for off-site backup.