That's a nice bench.
I've looked at it several times over the last few days and the only thing I can offer as a critique or an item of improvement is perhaps the arms and the back could/should have been tied together to offer mutual support.
As for a finish I'm partial to Watco Teak Oil for exterior projects. Easy to apply and a touch up every six months or so isn't that difficult. However that cedar will probably hold up just fine with no finish at all.
For six bucks I could have been insignificant on a popular forum. ---