Hi Victarion,
yes, a frame clip is actually a good idea.
Just I think it is more the rear hinge which benefits and less the belt.
In fact is the rear hinge the Achilles heel of your Strida - and sometimes even the real cause of belt issues.
On the SX shown above there is already an aluminium freewheel mounted.
The signs of wear on the freewheels teeth can be seen easily - is there still a narrow rectangle visible on top of each tooth or is it just a line, moreover that one can see a more or less pronounced corner at one tooth side.
The signs, without using a sharp eye, are:
- Belt gets loose
- Jumping, Skipping
- Twisting (often combined with rear hinge play)
- Torn
Tubes/tyres:
You may have noticed already that this is an enourmous advantage on your Strida; compared to most of the other folding bike brands - nothing more easy than to change tubes or tyres 
Sure, as long as it is not a burden for you I’d recommend a spare tube anyway.
I had the feeling in the past that Schwalbe tubes combined with Sclaverand valves are the best choice if you don’t want to pump air each few days.
Yes right, there are just the original Innova tyres, Schwalbe Kojak and another slick, the Strozzapreti of Joseph Kuosac.
Tubes are btw interchangeable between Innova and Kojak - but not Strozzapreti.
Counterquestion:
Do you want to ride in rain or on sand or cobblestones?
For the spokes you need a spoke wrench of your choize in size 3,2 mm plus a piece of wood (that can be a stolen old cook spoon of Mom or even a piece of branch) - and your ears 
Just knock on each spoke after another (separate; for example first the inner and then the outer).
Do you hear a clear tone (ignore the tone height)?
Yes → That spoke should be Ok.
Do you hear a dull noise?
Yes - > That one is loose.
By today I’ve got perhaps 8 or 10 original wheels in hands - usually there are between 1 and 3 spokes per wheel loose. But I think that’s better the newer the wheels are - maybe you find not a single one loose 
Cheers,
Chris