You should be concerned regarding the quality of the water you will feed the RO. If the water is hard or has iron the RO will require service much more often and you won't like that.

- Quality (how long is this going to last etc)
Can't go wrong with made in USA with USA parts. Pacific rims products can have QC problems that are a real PITA.

- Water Pressure (is it going to trickle out of my faucet...do i need to get a booster pump?...do i need to have a separate faucet for filtered water or can i just run all water in my kitchen through this)
You will have a separate RO faucet and the flow will be less than system pressure. Most people find it acceptable and in most cases the RO will supply a fridge and ice maker without assistance.

- Capacity (50 gallons seems good to me...)
Many people far oversize ROs. 25gpd is more than most will ever need.

- Waste (seems like a permeate pump will help with waste and with pressure, but i know there are systems that waste less than others
Waste is a matter of great discussion but those who actually observe their RO use and waste find there's little to lose sleep about.

- Cost (seems like a bunch of watts models are around 200 and i saw a tap master model artesan model for 400...)
The Watts models are appealing and they speak English when you call with a question. On the other end are the high dollar Kinetico ROs that offer some appealing features. In general, you get what you pay for but sometimes you don't.

- Replacing Filters (is it easy...how often...how expensive...etc)
Industry standard design ROs are easy to change filters on and they are available in lots of places so they are modestly priced. Proprietary ROs like Kineticos use proprietary filters and you are married to your local dealer which can be OK if your dealer treats you right.

Agree with justalurker....adding a few things from my own experience..........

Most RO systems use air-pressure holding tank. When empty, those tanks are typically pre-pressurized at about 8psi. When full (about 2.5 gallons) they are pressurized at about 30psi. Your output volume at the dedicated tap will be governed by that pressure. My flow-rate with my previously-owned air-tank system was about .6gpm when full dropping to about 1/2 of that as the tank pressure dropped off. I've seen similar flow rates with neighbors' systems. This flow-rate is partially governed by line-size and valve-size being used.

Refilling from empty against increasing pressure takes more time and wastes more water also. That's not bad, it's just the way things are. Some are better than others but they all do the same thing the same way.

There are more systems becoming available that are designed to refill without back-pressure. They refill faster and waste less. Worth paying attention to in terms of day-to-day convenience, IMHO.

FWIW.....I currently have Kinetico K5W which is pretty much at the highest-end of the home systems. The advantages of this system are 1) flow rate at the spigot is at household line pressure. At my 60-65psi line pressure, I get about 1.2gpm flow rate that stays level from full to empty. 2) Tank refills from empty (2.7 gallons) in about 50 minutes which is about 3x faster than previous air-tank model. 3) Tank refills with no back-pressure resulting in minimal waste as well as faster refill. These advantages are very worthwhile, IMHO, but they also come at a premium price. And, as justalurker said, I'm married to Kinetico. On the other hand, between softeners and RO's, I've now been with them for 19 years and their product and service performance has been exemplary. That performance and reliability I consider to have been worth the premium I paid.

(I have no relationship with Kinetico other than as a retail customer.)