First, this page offers a nice collection of wisdom: www.boox.net/topics/bicycles/external/stein.dommel.be/brompton/sections/Tricks.html
Mine is currently five years old and it's still a fantastically compact and manoeuvrable bike. Constructed mostly of steel, so it's certainly real and durable.
Climbing ease is determined by the gearing - mine is a 6-speed (distinct gears, no overlaps) consisting of a 3-speed Sturmey Archer internal gear hub (IGHs are in fact over a century old tried & true tech, but tried and true) plus a two speed derailer ("high" and "low"). Chain ring and sprockets are the reduced gearing variant, providing about 29 to 88 gear inches in range - plenty for most climbs and downhills.
Yep, but riding is the most fun way to get around. That said, most people live within very easy riding distance of a train station, so bike + train would be a potent combination.
No, not this one, but I do have another bag for it that's suitable for checked luggage.
In my opinion, the ride quality is better than nearly every bike you see. Great geometry, rear suspension block, comfortable riding position and good gearing negate any negatives that small wheels bring. Remember that small wheels does not equal slow (after all, cars have small wheels too)!
Maintenance is pretty straightforward, like most other bikes. On the chain, I've been conducting a WD-40 experiment since the bike was 3,822 km old - it's currently racked up over 22,108 km across a few chains (which tend to last a reasonable length of time - about 5,000 km per chain is what I aim for). No kittens have been sacrificed, so perhaps it's time for the anti-WD-40 hysteria to stop?
WD-40 References - read and try your own experiment:
https://bikefat.com/it-is-okay-to-use-wd-40-on-your-bike-chain/
Regarding other components, keep in mind that with a folding bike, there are a few more parts. This is generally not a problem, however just keep in mind that with extra moving parts comes extra attention that may be required to diagnose and troubleshoot clicks and creaks that may occur from time to time (just as you would any other bike). That said, quite often those creaks and clicks aren't even folding related - for example:
Pedals can creak! But which part? It turns out the screws holding the reflectors can come slightly loose over time and be the cause of quite an annoyingly subtle creak. Tighten up those reflectors before going about with unscrewing the pedals and cranks; that's all it might take.
The nut seems to be loose out of the factory (based on a sample size of a few Bromptons I've heard about) - just set it right and tighten it up. The best way to adjust a 3 speed Sturmey Archer is by tension in the lowest gear (greatest tension). You want just the slightest amount of play in the indicator chain. This almost always sets the gearing correctly and is easier to do than by sight.
Also make sure the rubber suspension block is screwed on securely.
The paint wearing away will end up making for a rough spot that the hinge clamp might get caught on. This can be sandpapered down and repainted with nail polish. Also note that the clamp might get stuck more easily in one orientation than the other. Draw a dot on one end and orient the clamp on the side it's less likely to get stuck on.
Use Kool-Stop Salmon Dura Ace brake pad inserts. They're the best and last a good while. Good for wet and dry, and they also leave your rims cleaner.
I've never had a puncture while using 35-349 Schwalbe Marathon tyres (the green ones, not the Plus). Similarly on my other bike, I've also never had a puncture with 700x28C Maxxis Re-Fuse tyres. The Marathons aren't the fastest, but they're a lot faster than stopping for a pathside fix...
Topeak Mini-Morph G. It's good. Can go up to 100 psi not that I need it with wider tyres. For the 16" tyres, I actually "underinflate" to 45 and 55 psi (front/rear). Read Jan Heine, Dave McCraw and Sheldon Brown to find out how much you should inflate tyres.
Going fast and countersteering is quite fun, but most of the time it's easier to just take it easy in busier spots. Learn to track stand - it's good training for balance and patience. Do countersteer often - it's better. Watch CagerOnTwoWheels's video to learn how to countersteer: https://www.youtube.com/watch?v=nlc1bGPTR3c
Wear a helmet? The issue is a lot more complex and nuanced than you might first think - consider https://www.youtube.com/watch?v=07o-TASvIxY
Also read http://www.aviewfromthecyclepath.com/2011/02/all-those-myths-and-excuses-in-one-post.html and http://www.aviewfromthecyclepath.com/search/label/helmets
Is not wearing a helmet on a cycle path in a park really more dangerous than wearing a helmet in peak hour traffic while being clipped in and head low with drop bars (even when riding in the hoods)? I see a lot of riders skimping out on spending money on accessories - quite often they will buy a helmet, but not lights for riding at night. Think about this.
In good conditions when you want to slow in a straight line, use 100% front brake. Yes, 100%. Read https://sheldonbrown.com/brakturn.html and https://janheine.wordpress.com/2011/04/13/braking-technique/ and then gradually practise it.
WD-40, Helmets, and front brake usage. The three most controversial aspects of cycling - do your own research and keep practising.
More to come... Need to collect more hours, kilometres and experience - when was the last time you rode a decent amount?