Folding Bikes - Was just given (almost) a Hon folder

A buddy of mine came by and dropped of a Hon folder. In pretty good condition.
We trade off doing things for each other.
I am really suprized at how rigid the frame is considering it folds so fast & easily.

It is a 16" wheeled one with a Sturmey Archer hub. Has the thin chrome braces that run from the top tube up to the stem. Need the upper section of the 2 piece seat post. I guess Dahon still carries parts for these ?

Now that I have it, are there any weak areas with these bikes that need to be addressed?
I plan on changing it to drop bars after modifying the stem and doing some other tinkering.

Recommended tires that roll nice but won't break the bank?

Anyone here do any semi serious distances on these? (10-20 miles)

I'm looking forward to getting on the road .

Yes i have ridden to church and back which is a 16 mile round trip.I have done this on the very bike you describe , although it has been modified to a 64 inch geared fixie.I have also ridden this bike on a 10.8 mile paved trail loop over ice and snow in the winter with no mishaps.A Dahon forums poster modified his 16 inch piccolo ? and uses it to tour .I do not believe he does 100 mile days but probably at least 30-40 or more.Check gaerlan bicycles for the tires you need . I think 305 by 1.75 in will be about the biggest you can use. I use schwinn knobbies rated to 65 psi . I recommend switching to a rear alloy rim.(Have it laced to your 3 speed hub in place of the steel) This should benefit you greatly ,as the reduced rotating weight will make pedaling easier.Also get a better saddle than stock ,I recommend a good sprung saddle . Perhaps you can purchase one cheaply as a take off at a local shop.