The time in making the top piece with the integrated barbs is insignificant. Really. The material would start out as 1" thick stock & the barbs are planned to be 3/4" tall. Now, a consertive estimate on removing the material start to finish would be 2 minutes, if that. Aluminium is fun to machine. "Typical" feedrates start at about 100 inches per minute, at least on the machines I have access to. I am still amazed to this day at how fast I can turn a block to a pile of chips on them. As far as deflection, a 3/4" length of cut is fine for a 3/8 carbide endmill, which would easily fit between the barbs. Funny thing is, it will take the finish tool longer to cut than the roughing tool. Most of the material would be removed with a 1/2" or 3/4" roughing tool, like this one...
For the tapered inlet plan, I really don't think that the typical 1/4NPT barbs are an option, unless I want to make my own barbs
The machine I will be using has 30HP? ( not totally sure on that rating, but it is plenty ) & a 12,000 RPM spindle.