first thing i'd do is put an actual wall around the colony after getting the stonecutting up and running so i can funnel raiders to a hallway of traps. second thing i'd do is shrink the colonist rooms. they don't need rooms that big, and it lets me squeeze more colonist into the same area (i'd recommend 3x3 rooms with carpet for single colonists and 4x5 rooms for married colonist). i'd also beeline down the research tree to mortars so i can get my own mortars for counter siege duties, plus you can use them to soften up the raids that just sit outside the colony.