backup battery charger circuit help

[babylyn90]

Hey guys, Desiree here from 2265. We're trying to build our own backup battery charger based off the circuit we found posted on another thread. A few questions came to mind since we can't seem to find some components:

1.) I was wondering if we'd be able to do series connections with some of the resistors in a way that would add up to the needed voltage. In example, combine 1K, 200ohm, and 40 ohms resistors to make the 1.24K in R3.

2.) Are precise values necessary? In example, could I use 220 ohms instead of 221 ohms for R2?

3.) I can't seem to find the zener diodes either

4.) Does it matter what I build the circuit on? Recommendations?

I'd really appreciate it if you guys could post either with links or tips to other threads/posts i might have missed. Thanks and sorry if this was already posted, i probably missed it!