Estate agent contracts tend to be 6 month, with private being 12 month. This is because estate agents will charge a few hundred to print off a new contract and pop it in the post to you. Beware of the costs involved with estate agents - for my £575/mo house it cost me well over a grand in fees, then there's the deposit on top...
Estate agents ALWAYS do a credit check. You *may* get around this by acting as a guarantor if your credit history is clean.
Sheds won't be a problem unless you want to slap a concrete base down. Putting a garage up would be a no-no though. Interior modifications are down to the specific contract. My last house I couldn't even hang a picture on the wall, but this one I can even paint!
For a first house for a skint person, furnished may well be the way to go. You can't upgrade anything later though. "White goods" means fridge, washing machine, etc and if you're going unfurnished you REALLY want to avoid having to put up with the landlord's white goods. My washing machine broke down the other month. Took nearly 4 WEEKS to get it repaired. Could have done it myself in a few hours, or given how much we really really need a washing machine I'd have rather just thrown it out and bought a new one than wait a month!

It took a few weeks to get the heating fixed when my little guy was only a few weeks old too! That's with an estate agent. With private landlords you're entirely at their mercy. At my last place I lived for years with mouldy walls and a cracked bog which I couldn't clean (it was only the limescale holding the water in!!!).
If he can afford it, go unfurnished, even if he has to spend the first six months using deckchairs instead of a sofa. I did that once - the wooden seaside type are surprisingly comfortable!
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang