This is hands down my preferred play style.
For the "point blank" situations as you call them, I feel it is a common misconception people seem to have about the play style. There seems to be a stereotype that if a thief/assassin is not fighting from range with a bow or using a sneak attack they are vulnerable and weak. This is completely false. In these situations what I would do is switch to my dual wield daggers (or your 1h of choice), I always make sure I keep my weapons poisoned with alchemy. Alchemy is a huge and often under-utilized aspect to this play style. It if course take forethought and preparation but that is one of the things I really enjoy about it. Also there is no reason that magic should be forbidden. I don't care to develop this significantly but I don't consider it taboo either. My plan is to stick with primarily just the Illusion tree as I think it will offer quite a few spells that will compliment the play style well (i haven't seen the full spell lists so can't say for certain if I will do this).
As for perks, I haven't looked through the full lists, but I have heard or seen a few I defiantly plan on getting. The x15 sneak attack dmg with daggers.... hmmmm yummy

, move silently while in stealth, etc
Pretty much I plan on focusing my perks for these skills in order from most important to least important. Of course this is subject to change since I don't know the full lists yet.
Stealth
Lock-picking
One Handed
Illusion
Marksman
Alchemy
Speech
Light Armor
Smiting
Enchanting