New Hawken HE1100 or Used Johnson "Big John" - and other questions

I have the opportunity to purchase either of the following for under $3500:
--New Hawken HE1100 (4000sqft) full warranty (no pump or accessories) $3500
--Used Johnson Big John, 6yrs old (10,000sqft) NO warranty (includes pump) $3000

Which should I buy?

I have an old 2 story farmhouse with newly poured basement built in 1900.
Each floor is about 800sqft
--New windows, original insulation, 3 layers of siding
--New gas high efficiency forced air furnace w/3 ton AC
--New gas high efficiency hot water heater
--The home is surrounded by flat farm fields

1. Is there such a thing as "buying too big"?
2. Which brand has a better reputation?
3. Will the Hawken be enough for the house and maybe hot water heater?

Installation:
1. How tight can you bend pex-al-pex in the insulated tile enclosure?
2. What is the best place to get quality insulated pex-al-pex?

Sorry for all the questions.. but thanks in advance!