Everyone here has already given good advice, so I'll just throw in my 2 cents, FWIW.
IMO, SP and MP are both fantastic platforms, depending on what you want to do. Personally, I use SP to theorycraft and test build viability. The higher drop rates, /players setting, and PlugY's shared stash and built-in tools--as well as the infamous "d-word"--make it a great platform for this. At the same time, I use MP to put what I've tested into practice, interact with other players, and listen to new ideas I may not have considered before (gear suggestions, strategies, build possibilities, etc.). There's also a thrill that comes with a new ladder reset that you just don't get with SP. It's like running a 10k. You find your bracket (in this case, choose a character/build), maybe chat with a couple familiar faces you see in the crowd. How's life? What sort of shoes are you using this year? That sort of thing. As you all move up to the starting line, the banner comes into view. The conversation dies down. In the distance, you hear a fading "good luck" as your buddies--who are now your competition--push their way to the front. You do the same. You watch the countdown timer with nervous anticipation. 3--you put your hand on your stopwatch. 2--you get low. 1--you lean forward. Bang! The starting gun fires. As if by instinct, you hit the button on your watch and you burst across the line, elbowing others around you as you try to break away from the pack. From here on, nothing else matters; it's just you and the road.
As for being a brand new player starting a week before a reset, my suggestion is to start on MP. IMO, now is the perfect time to start. Servers aren't bogged down, items are cheap or free, and there are still plenty of people online willing to help a noob out and show you the ropes. Understand that during the first week or so of a ladder, people are rushing to achieve their goals for the season, so taking time out to help a noob with Volrath isn't a priority for them; they have their own things to worry about.
and delete items that trade 
