Before you go and buy any more newts, please do some research. There´s some things i feel you need to know first in order to make a decent decission.
Both the H.orientalis and Pachytriton at the shops are all collected from the wild in very large numbers and under bad conditions. The importation process takes hundreds of lifes and those which survive are stressed and have been exposed to all sorts of things. Pet-shops usually make things even worse by providing negligent care (inadequate temps, bad water quality, mixed with other animals, etc). By the time they arrive to your home they are a mess...their inmune system is often completely shredded to pieces and it leaves them very vulnerable to infections, parasites, etc as well as many other problems. Flesh-eating infections are particularly common and among the most heartbreaking conditions to observe.
The problem is that finding captive bred alternative is impossible for Pachytriton and can sometimes requiere patience for Hypselotriton orientalis. You can find orientalis from hobbyists who breed them and also occasionally from larger scale breeders. Those are usually offered as juveniles and re pretty small which makes them more difficult to deal with than adults, although clearly not impossible. It just requieres more patience and a bit more experience. The Pachytriton have never been fully successfully bred in captivity (some people managed to raise them to juveniles but they then died inexplicably) so there is no chance of finding any from breeders. Every single one you see has been taken from the wild and imported.
I would very strongly advice you to look into captive bred animals instead of buying more orientalis from the shop, although it´s obviously up to you.
If you decide to buy more Pachytriton, consider two things. One, the more prepared you are and the more time you take to read about them, set everything up, etc, the more likely that a WC animal will have a chance to adjust. And two, Pachytriton are highly territorial and therefore can be extremely agressive and choosy. Some combinations work as long as there is enough space and visual barriers, others don´t, no matter what you do. This is important because you might find that the new newt you bought needs yet another tank because cohabitation is impossible. There´s no way of knowing before hand if the two individuals will tolerate each other or not.
Sorry for the rambling but i feel this are important things to know before you make new decissions.
As for substrate, gravel is a very bad option, it really is. Sand is very good as long as you don´t use a thick layer and there´s always the alterntive of going bare bottom which may not be aesthetically pleasing for some people but is certainly the most practical and easy option. Either species would be fine with sand or with no substrate. Plants don´t make newts mate, hehe, they are just egg laying substrates for them. I honestly wouldn´t worry about plants which are suitable for egg deposition just now.
Check out the articles in my signature there´s tones of excellent information there that i´m sure you´ll find very useful. Also check out the Cynops and the Pchytriton sections in the advanced forums, plenty of good threds there. Read until your eyes bleed xD The more you read the better you´ll be prepared and the more enjoyable the experience of keeping newts will be.
