Welcome to Infinity and congratulations to your faction choice.
My experience with Infinity might not be that great so far, but there are some points you should know/consider about your example list.
ParaMedics and Doctors sound good, but - in my eyes - as long as you do not have bigger amount of costly 1+ wound models on the table they're not of that big use.
Especially the Paramedics since they do not roll on
WIP but PH -3 instead.
Meaning the Line Kazaks would roll against 8 when trying to heal someone and if the role fails all orders would be spend for nothing.
Since the "112 Emergency Service" is quite cheap (and a real doctor) you could stick with him and give it a try for some games. Mine usually stays in the vitrine these days.
The Line Kazak with Missile Launcher is OK but as well quite expensive for what you get (e.g.
BS 11).
I would consider taking something else instead.
If you aim for the template, have a look at other options like Tank Hunters or Scots Guard or Briscard (but this is a heavy rocker launcher). The're all somewhat more expensive, but as well you get more tools like camouflage or
MSV 1 (and a better
BS).
If you aim for the punch, one one the nicest options for Ariadna is the Tank Hunter with autocannon.
Alternatively consider taking a (
AP)
HMG. It's as well
DMG 14 and has a bust of 4.
If you are looking for something heavy hitting in the
ARO you should have a look at the panzerfaust as well, which is available on Moblots and Minutemen for Ariadna. Both BS13 but no other special gimmicks.
Your lieutenant coice.
Well, the Highlander Greys are nice, but I consider them - since they are frenzy - offensive troops which can be against a lieutentant choice but this depends on your play style.
If you want your lieutenant to mainly stay in the back of the battlefield you should better give the Line Kazak lieutenent a chance. He's only 9 points instead of 30 and comes with
WIP 13 instead of 12 (Highlander). A Highlander staying behind would be a lot of "sleeping" points.
In addition the Line Kazak can be hidden among the other cheer leader pretty well.
Other alternatives:
Vet Kazak as lieutenant, but it's a very popular and obvious choice.
Tank Hunter as lieutenant: camo,
ADHL,
WIP 14 --> nice
Scout: camo, mines,
WIP 14 --> nice
Briscard:
WIP 13, marksman rilfe,
MSV 1, quite cheap --> interesting to cover deployment zone
Scots Guard:
WIP 13,
AP marksman rifle, quite cheap --> as well interesting
Or if you have SWCs to spare, have a look at the lieutenant option of the Foxtrot Rangers
etc
Other things:
Chasseurs: I'd like to max out their number on a vanilla list (=2) and take the Minelayer version if I can spare the points (1 more point and 0,5
SWC). With Sixth Sense, Camo and Flamethrower they are just very nice.
Adhessive: Ariadna has a good availability of nasty glue throwers in my eyes and you should always have them in mind when making lists. They're good to counter big enemys (
TAG,
HI) or just to annoy your opponent.
Tank Hunters can have them as well as Loup-Garou and Chassuers. In addition the Dozers can bring a "ADHL Panzerfaust" for just 19 point (and 0
SWC).
OK, I think that's enough input from my side so far.
ARIADNA
10 
0 
0
LINE KAZAK Rifle / Pistol, Knife. (9)
112 Light Shotgun / Pistol, 
CHASSEUR Rifle, Light Flamethrower, Antipersonnel Mines / Pistol, Knife. (19)
HIGHLANDER GREY Lieutenant Rifle, 2 Light Shotguns, Grenades, Smoke Grenades / Pistol, 
VETERAN KAZAKS (
TANKHUNTER Autocannon, D-Charges / Pistol, Knife. (1.5 | 40)
VOLUNTEER Light Shotgun, Light Grenade Launcher / Pistol, Knife. (0.5 | 11)