Ok, so you're getting a new tank.
Here's a step-by-step guide how to set it up:
Day 1.
1. Wash gravel/sand and put on bottom of tank. Alse place any stones/rocks/caves etc that you have available at this time.
2. Place pumps/(outlets), heaters, etc in the tank.
3. Pour in de-chlorinated water (I use Stress-coat, but other dechlorinators seem to work well too). You can use some water from an established tank, including some of the mucky stuff from the bottom when gravel filtering.
4. Turn on pumps, heaters etc. Leave alone for at least 24 hours.
Day 2.
5. Take the filter material from the old tank, squeeze into the water in the new tank, maybe even rinse a few times. YES it will make it look VERY mucky! This will add the beneficial (good) bacteria from your established filter to the new filter and the substrate in your tank. Leave this to clear [if you do it at night, you will spend the time waiting sleeping, which is always a good thing].
Day 3.
6. Place out your plants.
Day 4.
7. Add some of the fish. The most sturdy/hardy ones would be the best ones to start with. Leave alone for a couple of days. Give only reduced food.
Day 6-7.
8. Check water quality. If ammonia or nitrite(NO2) are present, the tank hasn't got a full set of beneficial bacteria.
9. Once the tests show no (noticable) levels of ammonia or nitrite, you can add another lot of fish.
10. Keep checking ammonia/nitrite levels, daily or every other day, depending on results (if there's big changes from one day to another, it's a good idea to check again).
11. Once the levels are stable (i.e. no nitrite or ammonia showing up for a few tests in a row), you need to start checking the nitrate level. If it rises high, you need to start changing water. A level of 25 ppm (mg/l) is a good "max" level to aim for. Lower is better, but too low will affect plants ability to grow.
Best of luck...
As to "common pleco" liking plants, I guess it depends on several things: They aren't the best plant carers in the world, they tend to bulldoze down plants when moving around in the tank. They often have their own idea of where plants should or shouldn't be, which may not match the owners idea...
Other than that, they normally leave plants alone, but sometimes they do EAT plants too...
--
Mats
wooooooooooooooooow hooooooooooo, 
bless them, 