Well, the two WD Blacks are going to consume something like 20W between them when active. The Synlogogy consumes another 10W or so. Figure 85% efficiency on the switch supply for it and you get 35W. The RT-N66U draws about 12W under high utilization. The TP-Link switch has a rated input power of 60W max. I don't have one and I couldn't find someone who had measured it online. Similar switches pull 50-60% of their rated input power so figure about 35W when heavily loaded. Picking one of the current Motorola SURFboard modems (modem only), it clocks in a 10W.
All total, that puts you at 92W. I wouldn't bet surprised if you measured around 75W. Remeber that the power draw will vary with activity. The two drives with vary three to four watts combined between idle spinning and active read write, the access point will vary depending on CPU load and radio utilization, etc.
A 600VA UPS should give you a 30min+ runtime if it is a quality UPS.
Simulated Sine Wave: CyberPower CP600LCD
True Sine Wave: CyberPower CP850PFCLCD
Everyone has their favorite brand of UPS. I've used APC, Belkin, and CyberPower. APC in kind of the gold standard though their basic home UPSes aren't much better than anybody else. I run my desktop on an APC Back-UPS ES 750. Their bigger systems are expensive and built like tanks. The Belkins felt cheap and were scrapped. I run my server rack on a CyberPower 1500AVR and will likely be purchasing another soon.