Congratulations Alexandria!
I popped my female sim down on the empty lot two up from Ms Crumplebottom. Traits I gave her were - Artistic, Ambitious, Loves the Outdoors, Perfectionist and Virtuoso with a LTW of Master of Arts. You see, I thought that in order to be able to paint a portrait of anyone, they either had to be a member of your family or friends with you, and I thought that playing guitar was a good way of getting multiple friends at once.
I learned Painting on day one (was the cheap lesson) and then went and painted and played the guitar around town. I painted small paintings until I got to level 7. Then I switched to large portraits. After the first few portraits, I managed to supermax painting and continued to paint away.
Another thing I discovered through play was if you are able to invite one sim of a multi sim household over (using invite household over interaction) more than likely, a number of them would come over, I could lock the gate after them and keep them with me for as long as I liked! I also liked to trap the paper boy/girl using the same process, 5 of my portraits were of paper boys/girls.
My finishing stats were 44 paintings, 9 brilliant, 13 masterpieces and 24 portraits. I supermaxed painting, and reached level 8 on guitar and painting career (I sold the paintings, but not the portraits) I had acquired 110k in happiness points over the four week period (without completing the LTW) and bought immune to heat, extra creative, hardly hungry, dirt defiant, steel bladder, fast learner and eye candy.
I had given myself a target of 20 of the portraits, and so I was happy with my effort of 24.
I did research into painting, primarily reading through the painting guide here on Carl's and also going to the Sims Wiki site and printed out their information on painting and did a practice run. I did up a spreadsheet with 3 columns, first one with sim name, 2nd one with whether or not I painted their portrait (when I started their portrait, I assigned a number, when I finished I wrote yes) and 3rd one with the value of the portrait.
Anyway, that's how I did it, thanks again to Marion for the idea and to the team for implementing it!