I can't make up my mind though. On eBay a lot of people are selling shellac to move to another system ?
ebay shellac is not original, it's cheap chinese fake shellac-wannabe. I also bought a couple from there when I first started and I didn't know the difference. Well the difference is in the chemicals used. ebay's are much stronger and could harm your nail plate after prolonged use. I binned mine about 2 weeks after my purchase.
I can't talk of OPI as I only use their lacquers.
But I use both shellac and gelish and I have now started with iLac
Gelish is a pure gel polish, which means it suits all types of nails as it's a bit stronger, but to apply you need to buff the nail plate, hence weakening the natural nail every time. Gives on average 3 weeks wear time.
Both shellac and iLac are hybrid gel polishes, meaning their consistency in gel is smaller than pure gel polishes. It's great for strong healthy nails but doesn't last well on weak ones. There are many ways to counteract that however, like using a strengthening gel underneath. Anyway, being hybrid gels, they don't require buffing of the nail bed, thus safe-guarding the natural nail. Gives on average 2 weeks wear. Both brands are fabulous, iLAc is cheaper, because they don't work with distributors and they manufature all their products in England.
It's basically what you care most about. To help your clients grow strong natural nails, or to keep their polish for longer.
I'd start with trial packs of all three to be honest and move on from there. Or find a couple of salons which use these brands and have yourself a manicure and see how it feels. There is no right or wrong answer here, you just need to see what suits you best. Not every tech can work with every brand. I, for example, don't get on well with gelish. I do use it yes, but I don't have many colours yet and I haven't practised as much as I should.
As to the lamp, well there is no easy answer when you start. I bought myself a CND one as it's the brand that most techs work here with and it's what people ask for. So, now I mostly use shellac. When I inquired about iLac though, I explained that I wanted to try their system but no way would I buy a whole new lamp out of the blue without trialing it first and asked whether it would work with my CND one. They replied back explaining what I had to do to make it work. I did the same with gelish here and the distributor had no idea what to answer me as they don't bother with "light wavelength here" and "a led lamp with xx secs is only what you need". The lady couldn't help me because she herself wasn't informed. So I did my own trial and it worked fine for a while. Is it ideal? No, it's not, as I can't guarantee my clients their 2- 3 weeks wear time but it's ok to try it out for some time. Not to mention that no insurance will cover you if you mix and match systems.
My point is, I know it's not easy to choose. And you are bound to make mistakes and spend a lot of money on trialing things. I see you have made a whole bunch of threads asking what to do and what to buy. We have all been there but no one can give you a definite answer. You need to do a lot of reading, see what's already been posted instead of asking for someone to tell you what to do.
If you want my advice, stay off ebay when it comes to chemicals. It's ok for glitters only and whatnot.
FYI, given the choice now, I'd start with iLac, since it's cheaper and the only vegan brand I could find.
Or shellac if you can find a decent offer. I know S2 have offers on regularly.
But get all three trial systems and see what works best for you.