The single thing that makes gel nails last is prep. Not the brand, not the lamp, not the colour. Everything that determines whether your manicure holds for three weeks or lifts by day eight happens in the ten minutes before you open the bottle, in steps most people skip.
The two services generating the most consistent client demand in Ireland right now are gel polish and BIAB. If you build your starter kit around those two and nothing else, you have a full working service menu.
The fastest way to make at-home gel nails last longer is to fix your prep and your product system, in that order. Most guides stop at prep. Prep matters. But it's not the whole problem.