The correct figure for insolation in the DR will be around 5.2 in the worst month and 6.5 in the best month. You can find simular data by googling insolation chart (will probably not have non US data) or look at the worst month insolation map at
http://www.sunwize.com/info_center/insolmap.htm
A tracker will help some, but they generally do not pay for themselves and are prone to mechanical troubles and serious wind load troubles. They help most in Northern climates. In no case will you get 8-12 average good hours of sun, the atmosphere prevents that from ever happening, anyplace on the planet.
You get the number of amp/hours per day produced by multiplying the rated amperage by the insolation number. The insolation number is the theoretical number of good sun hours per day, on average. Most systems should be sized for the worst month, but in the DR, with A/C you may wish to size based upon your summer load.
Typical economic paybacks are generally 15-25 years. This number can be reduced by going through your condos and replacing high load items to be run off of solar with more efficient models; ultimately this will make the needed solar system much cheaper and will more than pay for high efficiency appliances. Refridgerators are a great place to start. Replace electric hot water with solar or gas.
Once you have a good figure for the amount of energy you need per day (in kw/hrs), divide that by the insolation value. Then divide by .85 (figure an 85% efficiency) and you know how many watts of panels you will need. Your installed cost will probably be around $6-7 per watt for the system, figuring US prices, low labor costs and a wholesale cost. This would be for the batteries, inverters, charge controllers, panels and locally fabricated mounts, etc. To size your battery bank, figure the number of amp/hrs per day and the number of days you will be without sun then multiply by 2.
You should have a planta for backup use, sizing your batteries for a worst case situation will cost more than a modest planta. Or plan on street power as an occasional backup. Most solar electric systems are designed to provide all electric needs 85+% of the time, very few are designed for 100% of the time.
They array size should fit on the roof of the condos without trouble. The panels would all need to be in good sun, not a single tree branch etc.
Panels come with 10-25 year warrentees. I have never heard of someone claiming on one. There are many panels older than 25 years which still output most of their original power. The only normal failures are due to weather damage.
Inverters are not particularly reliable. In your case you would want an array of inverters such as exceltechs, which have multiple redundant components; the mean time between failures is around 15-20 years on these compontents and it can lose one or more while maintaining continuing to function. They are more expensive than Trace, but also more reliable.
Batteries will vary with brand and use. Figure 3-20 years. Rolls and Shurette (?spelling) make very durable batteries, but from a cost point the best are probably Trojan L-16 HC's. If treated well (EDTA will help) these can and do last 15 years at the high end. Untreated Trojan T-105s (what I saw in the DR for some peoples inverters) may last only 3.
Charge controllers are pretty reliable. You would probably want MPPT controllers which will nurse every last watt from the panels. You will be able to have high voltage (96, or whatever) arrays and still use a sane battery pack like 48v or 24v (these are nominal voltages, working voltage is higher)
If you actually do this, you will want to fly someone with a lot of experience in large installs down from the US. You are talking about a very large system, if its for a whole condo complex, even most professionals in the US have not done an install this large.
Also, many people fail to consider the likely $/kwh of electricity over a systems lifespan, as opposed to what it is today. No one can say what electricity will cost in ten years, but it is fairly safe to assume it will be quite a bit higher than today (based upon fossil fuel demand vs supply prediction models).
Hope this helps.