It sounds awkward, yeah, I would go with the indirect construction for the last phrase:
"If you have enough money, it is possible to buy not only a new car, but also a new house."
Anyways, for the first paragraph, the best way to figure that stuff out is to look at the tense of the other verbs in the paragraph. "Christopher Reeve IS" and "at first, he could not eat solid food, but now he CAN" are the indicators that you should use present tense. Be careful with phrases like "Reeve WAS also an experienced horseback rider." It's in past tense, but it's referring more to Reeve's horseback riding ability than himself personally.
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_foolmo_
'Oh please, if foolmo made that analogy you'd think it was picture perfect' - Biolizard28