There's not much wrong with S/H bodies if you find a good one at a good price. If you shop around, not just on ebay, can pick up bargains Decide what you want first then shop. I've had Nikon, Pentax, Canon and gone back to Nikon.
Read the specs. Make sure it hasn't got a high shutter count. 25,000 shutter actuations is still pretty low for a S/H body. Also as mentioned AF motor in the body. Aperture coupling ring would also be a bonus. This would open up the variety of lenses available.
As mentioned D3100 is a good buy though accessing some of the menus can be a pain and time consuming. Same can be said for the D5000 and D5100. You don't need mega, mega pixels unless you're blowing your pics up to AO size... 12MP is just fine for every day use and will enlarge to A1 no probs as long as the glass you're using is good quality. I'm just as happy shooting with my old D90 just as much as my D7100. The D7100 IMO is one of... Is the best DX DSLR on the market and if you shop around you can pick them up for dirt.
Advice Alway use same make lenses. They always work and are faster at auto focusing.
Kit lenses: Some good points. Some bad points. The Nikon 18-55 and 18-105 have plastic lens mounts so be aware they can break if knocked. I've done my 18-105 mount several times and repaired it several times. (You can buy a repair kit for about £4.00 and it takes about 20 minutes). Then I bought another. Reason: for a budget kit lens it's tac sharp all the way through the range. A fantastic budget lens as long as you look after it.
Apart from the Pro lenses I have, if I travel I take two lenses. The 18-105 DX lens and 70-300 VRII. The later is an FX lens but gives coverage of 105-410mm on a DX body.
Word of warning. Once you start on the road to SLR and DSLR you can get hooked.