d, For bird houses and other outdoor items, you should consider a finishing nailer as opposed to brads. Brads are normally only 18 gauge (very thin), and have almost no head at all, yielding very little holding power out in the elements. Finishing nails are heavier (15 or 16 gauge) and have more of a head. Primary use for brads in bird house construction would be to hold the wood together while glue sets up ... and clamps will do that job better. I have both brad & finish nailers, both Campbell-Hausfield, and they're okay. I don't use 'em a lot, but I have had them for 8 years or so, and total usage adds up to quite a bit. No problems with them.

I'm going to also say at 5/16, you should probably be gluing the flooring in place as opposed to nailing it down. The reason for this is that when nailing flooring in place you are really on using 1/2 the thickness of the wood for maintaining structural integrity. This is because the nail sits in the groove of your tongue and groove flooring. I personally wouldn't my flooring being held in place by nail only going through 5/32 of an inch.

Redwood,cedar, cypress are all great exterior woods. Personally i wouldn't put one spsecies over the other as they are all great.Redwood and cedar hold a close resemblence, cypress differs somewhat, so it's a personal decision for you what would look the best for your project. As far as fasteners,i would dump using nails and go with screws. Double hot dipped fasteners are claimed to be free of staining, but if it's in your budget, i would go with stainless steel. Here is a link that might be useful: nails and screws

I have the Ryobi 18 gauge brad nailer from HD and have found that it works really well. It is far easier than using a hammer and nail and trying to keep trim aligned. https://www.homedepot.com/p/RYOBI-18-Volt-ONE-Cordless-AirStrike-18-Gauge-Brad-Nailer-Tool-Only-with-Sample-Nails-P320/203810823 The very small holes it leaves where the brad enters the wood are easy to hide with caulk or wood putty before painting. I've used a variety of brad lengths, including 2" brads when I had to go through a doorframe, drywall and into the framing underneath. With the longer brads you need to ensure you have it aligned correctly so the brad doesn't take diagonal path and come out the side of the trim. Ryobi prices are kind of unrepdictable, and sometimes you can get a much better deal when purchasing the tool with a battery and charger, or when you purchase two tools in a combination pack. The Ryobi batteries I've had for a while (3-4 years) seem to be losing charge more quickly, but some of the newer tools come with better batteries, or are brushless (consume less power). Bruce