You are on the right track for the least expensive way to get into this thing called competition. Multiple cookers can be a benefit but aren't necessary to get into a cook off. Same with multiple woods, etc. some do it but most have one blend they use for all the meats.
Spice's cookers have good solid wheels so if you got the ramp go for it. Some teams cook tons of food - but most do 12-18 pieces of chicken, 3-6 racks of ribs, 2 pork butts, and 1-2 brisket. Tim and I throw a couple of fatties in for breakfast but we don't cook for a mob.
We have plenty of "left overs" to pack up to take home.
So, what I'm saying is: the medium Spice cooker will probably do it for you. If not, get a WSM to round out your artillery.
Just my $.02.
Southern Brethren BBQ Competition Team
"It's all about getting paid!" - Myron Mixon
"I love being hated in my hometown!" - David Hair
KingFisher Gator Rotisserie cooker, WSM, Stainless 5 burner with IR gas grill, Turkey Fryer, Weber JD Commemorative grill, slightly used Bandera chamber for future use as a cold smoker, Masterbuilt 40" insulated ELECTRIC smoker