Answering point by point:

You will be very lucky to find a small car with a full sized spare, most have no spare at all.

Some do, some don't, check it when you go and view the car, all you need is a tape. Alloy fits in the space saver well in our Kia perfectly.

All small cars have a small boot, its because they are small cars. If you need a bigger boot look at bigger cars.

After 5 years any car can be a lottery with regards to reliability but if you look after the car well it should look after you.

Many cars have push button starts and you still need a key or card to de activate the immobiliser. Not an issue in truth, if it was insurance companies woul be loading models so fitted.

With regards to the timing belt don't worry about it. Yes they need changing but the intervals are now much longer and the belts much better. Ford recommends 10 years or 100000 miles on the Fiesta engine. Chains are not fool proof, some makes have had huge issues with them. If the engine is properly maintained you will be very unlucky to have an issue with either.

Think what you really want because your needs and desires appear to me to be somewhat at odds with each other. For example manufacturers fit space savers or no spare to give cars a bigger boot (they also save them money and keep weight down a bit), you want a big boot and a full size spare. This is just not achievable in a small car, you will not find such a car on the market.

Even with a chain cam , preventative maintenance is advisable. Change the engine oil more often than is recommended by the manufacturer, use a flush and ensure it's drained from the sump (not sucked up through the dipper tube - even some main dealers do this). Many chains are lubed by oil draining back from th ecam chamber and this area can be prone to sludging, leading to oil starvation for the chain.

I have a 9-3 Aero. This from HJs car by car breakdown:
Petrol engined SAABs with 4 cylinder SAAB engines prone to sludging up of the oil feed to the balancer shaft sprocket. Essential to change the oil and filter every 5k miles, to flush the old oil, and to drain from the sump plug. Do not siphon the old oil out or you will leave sludge in the sump

I bought mine at 3 1/2 years and 41k. In 11k since I bought it I have done 3 oil changes with flushes. When I did the second one I left a litre of the drained oil to stand in a glass jar for 3 weeks, then poured out. 3mm sludge in the bottom of the jar. Repeated this test at the third change, no sludge. Another 3k oil change coming up soon.

I have always changed oil much more frequently than specified (and other fluids too, gearbox, steering, brake and coolant). In my rally cars we changed the oil after every event.

All my road cars have been modified and I like to use the performance. I like to keep my cars for years too. My 800 Vitesse Sport was with me 11 years to 165k. Took the cam cover off to show buyer - clean as a whistle. Oh, and on it's original turbo too. And I drive my cars hard (once warm!). Same thing with my 220hp quad SU V8 SD1 flier! over 100k, never so much as a hiccup.

The price of oil is small compared to engine or gearbox rebuilds.

You will not be disappointed with the Swift--a great small car, great fun to drive and much underrated.

I have a current SZ4. My last 1.5 GLX was 5 years old when I sold it and nothing went wrong with it.

I have a bit of background with Suzuki. They are a brilliant engineering company whose design philosophy is "lets make it simple,robust and powerful using proven principles" instead of "lets show everybody how clever we are"

All Suzuki motors are robust and well made, whether chain cam or belt cam, never known one break a chain or belt. The Swift petrol motors are great little motors, but the 1.3 DDis diesel I wouldn't touch with a long barge pole, although to be fair these are now being built under licence by Suzuki themselves instead of by Fiat, GM, and Uncle Tom Cobley et al in Asia.(head gaskets fitted upside down anybody?)

The problem with Suzuki GB can be parts supply - it can take a while for parts to turn up through their system.