Put some compost and/or quality mulch down now so it has some time to kill off any existing top cover and start integrating into the soil before spring. I have had good luck using composted cow manure as a pre-planting amendment. Use about 1-2 lb per sq ft (4-7 bags for your space) depending on how weak the soil is. Make sure you get the good stuff, pure composted manure, not "manure with compost". If you are really enterprising, you can take a sample of your soil down to your county ag extension and have it tested and they will tell you all kinds of stuff about it like nutrient deficiencies, ph, etc. Sand can be both good and bad as a base. It drains well, but if there aren't enough organics it won't hold moisture. If you can dig up a shovel full and see one or two worms you should be in good shape (though it is probably too cold to do this experiment right now).
150 sq ft is a ton of space, you will have more peppers than any human can eat. Make your rows narrow enough that you can reach into the center from both sides without stepping into the planted space. I like to set my plants in groups of 3 about 8-12" apart so as they grow up they make a little clump that lets the plants support each other in high winds. Space clumps about 4 feet apart, more or less, depending on the expected size of the adult plants. Other people like to grow a single plant every 3-4' to give each individual plant more space to try and maximize yield. YMMV.
As for varieties, I like to always have some Thai or Goats Weed on hand. I like to make sauces with Tabasco varieties (Tabasco also loves the heat and are huge producers). Every year I toss in whatever else sounded good when I was buying seed. Superhots can be heartbreakers, but it is very satisfying if you can get some exotic pepper to yield ripe pods.
Good luck!
P.S. If you are planning on any superhots, you should start your seeds indoors now and transplant in the spring to get a head start since they take forever to germinate.
