I am a 30 something father of 2, but an only child. We also live isolated from what family we do have, so I feel for you on that one.
First, forget about being too old, you're fine. You're fine to wait a few years and then have another too, so this decision doesn't have to be final right now.
There are obvious advantages to 1 that you mentioned. Costs, logistics etc all go up with 2. I had a great life as an only child and got a lot of things that my friends with siblings did not - travel, toys, computers, extra curriculars etc. There is no doubt if you only have 1 place to direct your efforts and resources then that 1 will receive more than if they had to share and you will have more of your life and money to give to yourselves instead of your kids.
I have never stopped wanting a sibling. My parents are both still around but they're older and when they're gone I will only have my wife and my own kids. I have no siblings to help pay for or care for them or to make critical care decisions. I am not close to my cousins, who are all also only children. As only children we're all pretty ok with this relationship. My wife says I have 'only child syndrome'. I have had to learn to share(and fundamentally I still don't like it), learn social skills, learn to be diplomatic, and learn to speak up, because growing up I mostly had only myself and my internal dialogue to figure things out. I am a very self centric person and this is a criticism that's been consistently said about me my entire life. Now, I am a lot like my mom in this way, who grew up with 3 brothers, and obviously being an only child doesn't make you socially retarded(except sharing imo), but it certainly didn't help.
As a parent, I was very opposed to stopping at 1 because of my life. My wife has a brother and their relationship could be better, so the idea was discussed with the backing of a lot of positives you mentioned, but in the end we are done with 2. We actually stopped at 2 for all the same reasons - for 3 we would need a new car, new house, harder to travel etc. We would do 3 if we could afford to wait a bit, but that would put us into the 'too old' area.
In hindsight, from the parenting perspective. Going from 1-2 is both very challenging and easier than you would think. You are not multiplying your current effort and frustration by 2. You're already good at this now and you have the baby stuff already. The biggest shock is going from the 2:1 ratio to 1:1 or 1:2 at times. Takes getting used to, but you're experienced, and the kids start to take care of and play together - my oldest is 3 and this is already happening. He's developing a brotherly sense that is totally alien to me, and totally validated my decision for more.
The 2nd one going from 0-1.5yrs....those were some extremely trying times, I can't deny that. No money, lots of work, forget travel, reset the clock on poopy diapers, up all night.... but it's clear now as the little one grows up that as siblings they're going to work well and take care of each other.
That's all we wanted for them; that they will have each other, for their own lives. Not just mom and dad.