I most definitely recommend heat plates! In fact, I've never used anything else, and now I never would. I brooded my first batch of ducklings 2 years ago under heat plates and loved them. Since then I've brooded 3 batches of chickens and 2 more batches of ducklings. No problems at all and so easy to use.
The heat plates come with 4 legs that are easily adjusted. From the very first time I used a heat plate I put the legs in so that the back end was lower than the front. That way the chicks found it easier to run under, and they could adjust their own temperature by moving wherever suited them. Warmer in the back, cooler in the front. I did find that some chicks seemed to hang out in front right from day 1, where some seemed to like the extra heat in the back. Nobody got pasty butt, and nobody ever acted too hot or too cold, it was perfect. I also didn't add lighting for the chicks at night. When night time came it was dark like it would be under a hen. They all went to sleep and there wasn't a single peep. Just a warning for you...if you've never seen a baby chick really zonked out, they lie on their side and they can look like they died. The first time I saw that I was horrified! Turns out it's completely normal, LOL!
As to when to raise the heat plate, that is just something that you will know by watching your chicks. Same goes when you first start out with a heat plate. When you see the size of the actual chicks it makes it easier to judge how high to set up the plate. As the chicks got older I started to straighten out the heat plate so that it wasn't tilted towards the back so that I could put a nipple waterer on top.
One thing I will say, I didn't trust the companies claims when they referred to how many chicks the 12x12 heat plate could brood (I had 22 chicks the first time), so I also bought a larger one (16x24) from Premier 1. I start off with the small 12x12 and when I'm ready to move the chicks to a larger area, or to an area in my coop I refer to as chick jail, I use the larger one. With the larger one I feel more confident that I can move my chicks outside and they will all have room to get under the plate and stay nice and cozy. I've put 22 4 week chicks outside in my coop under a large heat plate with night time temperatures of about 10 celsius, or 50 fahrenheit, and they all did perfectly fine. In fact, some of them chose to sleep on top of the plate, even when I tried to scoot them under, lol!
When I first started out with ducklings/chicks I remember being paranoid about them getting cold. Then I had a broody hen that I let hatch out a few chicks. Let me tell you, those little babies are much tougher than I ever would have guessed. They were out running around in cool windy weather at 6 days old, and didn't seem that fazed by it. They'd run under mom when they needed to but it wasn't nearly as often as I would have guessed. I also found that they feathered out much faster than in-house brooded chicks. A proper heat source with no drafts is vitally important but I question the "Ambient Temperature" claims that I read about when I was first doing research. Seeing chicks being raised by hens a few times now has made me a lot more relaxed in regards to brooding these days.
So, to finally finish this novel of a reply, I'd recommend a medium size heat plate if you think you'll be putting your chicks out and the weather isn't completely perfect. That should give them plenty of room for when they're older. Also, the heat plates are easy to use and stress free, more natural compared to a heat lamp, and no risk of ever starting a fire.
Good luck!
Hope some of this helps