Get the highest grade bike you can, in this budget end of the market, a few extra $$ buy you a lot of extra quality. Make sure it fits you well, esp in the reach from saddle to bars. You will need the advice of a good bike shop to get this right.
Replace the tyres with some high grade, kevlar-belted ones at the shop. You should just have to pay the price difference, and upgraded rubber is the cheapest and most effective way of improving performance and reducing punctures. Most hybrid tyres are too fat and knobbly for efficient road riding. A lightly treaded ones of 28-32mm will be much easier to pedal and can handle off-road trails with no problems.
Most hybrid saddles are way too soft and squishy. Harder saddles offer better support and are more comfortable, they just dont sell as well to newbies. Suspension seat-posts can develope a wobble after regular use, I wouldnt recomend them. I would second Alex's suggestion of the sprung Brooks saddle. This will smoothe out the bumps, and is a comfortable well proven design.