I am keeping a mixed reef now slowly going with more of the sps with the colors I like and some softies.I am running a kalk stirrer now and it is right on the edge of needing something more.
If your right on the edge then it likely will not take much 2 part to keep up in addition to your existing Kalkwasser. I'd probably at least start out that route. If it suitable/acceptable to you then just keep doing it. If you find it's too much day to day then move up to the CA reactor. I'd be hesitant to spend that much up front money until you have exhausted the possibilities. But not all people are that way and would jump right into a reactor without trying the others first. Choice is yours.
I think that is the only thing stopping now is the up front cost.But it does look like a reactor is the way I should go especially if I keep adding sps corals.I have seen some great looking tanks with both systems used.
Eventually you may get to that point. Until your bioload increases significantly 2 part in addition to your Kalkwasser will likely be sufficient.
It's always good to have 2 part around anyways so that you can make adjustments to your freshly mixed saltwater and/or one time adjustments that may be required occasionally when using a CA reactor. So if you start out with 2 part then go to a reactor later you will always find a use for it and won't go to waste.
Could also buy you some time to find a really good deal on a used reactor/co2 setup.
I agree that I'd start using a two part plus the limewater, and then if you get tired of that, you can either upgrade to a two part doser, or a CaCO3/CO2 reactor, if and when necessary.
Functionally, there is no advantage of a CaCO3/CO2 reactor over a good two part, and in fact a good two part may be better in that it may maintain magnesium better and may keep the pH higher, if that is an issue.
You said you were looking for opinions, so here is my 2 cents. I ran a geo ca reactor for 18 months. It was not set and forget. It was constant adjustments to the effluent drip rate and the bubble count and they always seemed to drift from were you set it. Every 5-6 months when the co2 ran out and you change the media, it seemed liked you have to try to dial it all in again, just when you were getting close. Now I am running BRS 2 part with dosers. I was running Kalk before and now. I strongly suggest as Randy and others above said mildly. Run 2 part with Kalk and occasional Mg dosing. Use salifert test kits often! JUST DO IT! Good luck!