Hydrotap is not available in the US and Australian companies won't ship to us here. Believe me I THOROUGHLY researched that angle even debated having it shipped to family in Australia and them bringing it but there would have been no warranty on it at all. We ended up with a RO sytem with an Evercold water chiller and an insta-hot hooked up to the same faucet. We purchased the system at cleanwaterstore.com and I think it came in around $1000 with the chiller, heater, ro system and the dual faucet. We LOVE ours

I also have been looking into making my own with mix and match components.

I'm not certain I know enough about the type of system you are considering. However, we have an RO system in our home and the components are located in the basement quite a distance from the kitchen. It works very satisfactorily. When the system was initially installed, the installer placed everything in the cabinet below our kitchen sink but it took alot of space so when we changed the sink, we had it moved onto a shelf we built in the equipment room of the basement. I only remember that it was necessary that a bit more pressure be added to the bladder to compensate for the altitude difference. Hope this helps.

While I am not familiar with the specific brands that you refer to, I believe that it is important to do both. We have a full house filter - filtering out the large particulates/silt helps all the big items that use water - our washing machine, our dishwasher, the toilets, the sinks. Since installing ours, there is much less mineral build up (we don't have to scrub mineral deposits from the bottom of the toilets nearly as often - usually only when we forget to change the big water filter when we should). From the reading my dh has done, it extends the life of things such as our clothes washer. We figure that the whole house filter is very much worth it right there. The tap at the sink is very helpful as well. Our water is MUCH better tasting, and you can tailer those filters to your needs. Different ones have different abilities. (Getting rid of cysts, lead, etc.) Regarding having a water filter in the kitchen, even if you like to drink filtered water out of the fridge (like my dh) I like to rinse my fruits/veggies with filtered water before giving them to my kids. I also use it in the pots when I boil pasta. Our water is treated, however it is initially from town wells, and I don't really trust some of the things our local water company has done. I don't want to think about it when I have a glass of water or brew a pot of coffee. What will you be doing at the bar sink? Any prep? Grabbing a glass of water? You may want a filter there. Where will you be filling pots for pasta? Filling a large pitcher? Filling the coffee pot? Or making Tea? While the initial cost may seem prohibitive, it should actually be a small amount compared to all of the other items that you are upgrading. And water is much more a "part of you" - If it was me, I would put a whole house filter in, a filter tied directly into the faucet where I was doing the most "prep" of veggies/fruits (that sink's main faucet - not a separate drinking faucet there - it is a bit of a pain not having a prep sink and only using filtered water out of our small drinking faucet) and a filter under the other faucet where the washing up was being done, but with a separate drinking faucet. That way you won't be filtering water that you are using for washing (which reduces the life of the filter). Or, you could always install one for now in the prep/bar faucet, and add one later to the other sink if you find you need it. Of course if you have granite, that may require another hole. So maybe you want to add one to the main faucet, and can always add another one to the main bar faucet (using a different valve under the sink) at the bar faucet. If, however, you think that the bar faucet will be your main drinking faucet, I would add a filter to both now. Sorry. You asked about two and I am recommending three. BTW, my dh, who is not all that handy, installed a water filter under the kitchen sink. He had some advice from a plumber friend. It didn't take...