Hey Panda - welcome to the smurf brigade!
I think if you are learning the basics then your list is ok and you will have a lot of fun playing it. However if you want a bit more variety and to make you opponents think a bit more then you can definitely tweak it to provide more of a challenge and introduce yourself to more aspects of the game.
Firstly - all the above comments are good ones and worth considering. Personally, at 750 points I would go cheaper on the
HQ to allow for more boots on the ground. The Libby also doesn't really want to be sat back babysitting
DEVs - he wants to be up in the action, either psychic shrieking units to death or rolling on biomancy and assaulting. In this regard, you could put him in an assault squad and either give him a jet pack or put them all in a Drop pod together (at no additional cost to the assault squad too

). This will give you a nice deep strike threat to keep your opponents honest.
Any spare points I would put into scouts - again, a cheap way of boosting boots n the ground but they can also infiltrate onto objectives from the start, and can hold their own if given a
HB and are deployed in some cover. I would also mix your
DEVS (not normally done, but it will give you more flexibility) to have 2
MLs and 2
LC for a bit more punch. Given the above, my revised version of your list would be something like:
Libby, Lv1, Auspex (rolling on Telepathy, joining assault squad) 70pts
Scouts x5,
HB (infiltrate onto objective in/near cover) 63pts
TAC x10, Flamer, Rhino (general purpose / some anti infantry threat) 180pts
TAC x10, Meltagun, Combi-melta, Rhino (general purpose / some anti tank threat) 195pts
Assault Squad x5, Flamer x2, Drop Pod (Deep strike threat + Libby delivery system and
LoS) 85pts
DEVs x6,
ML x2,
LC x2 (ranged Anti tank and Anti infantry plus a few ablative wounds) 154pts
747 points
Also allows you to use all the Ultramarine Doctrines to good effect at some stage.
Hope that helps!