What is your budget?

Mono or half deck? If half deck, what's the other half that you already have?

and as joeshmo said - what's your budget?

Avola, Oscar, and Moses seems to be an affordable mainstay for mono.
Ace and Spiaghi is definitely really useful be it mono or half deck.
Jimmy is good - proper damage and DR if you happen to lose.
Desmond and Edd Cr are real good 4*. Vito is useful for SOA.
Gianfranco, Sharon, bella are good 3* options.

Here are pretty much the cards to choose from for a Montana mono (in order of my personal preference):
2*: Spiaghi (great card, necessary) Ivy (poison = huge threat & potential) Prince Jr (Mini Mona) Ace (-16 = good)
3*: Mona (though probably out of reach) Moses (Damage) Oscar (9 Power) Giafranco (Solid) Sharon (Damage)
4*: (Note this is sec is by preference/need) Edd Cr (expensive but SOB) Desmond (solid) Donnie (DAM) Vito (Beginner SOA, though the worst out of the 4)
5*: Avola (Major DAM) Fabio (Round Wining Power) Jimmy (DR as fallback) Don/Tino (Don = nice dam + extra atk manip, Tino = cheaper, but worse, version of Jimmy)

Order list by price, ascending... I see:

Ricardo - Shit*y card but cheapest way to get DR so its play-value-per-clintz is OK for first deck.
Ivy - Best value for money hands down.
Orenichi - Good value, playable stats and usable ability and extremely cheap.
Paolo - Not very fancy but better than nothing. Worth his cost.
Ace - Good card if you need 2* - has decent pricetag.
Filomena - Ok card for 2*, especially if your deck lacks damage.
Aniki - Good card, decent pricetag. Definately good for beginner deck.
Tino - Heavy hitter and usable ability and reasonable price.
Desmond - Great card, still cheap for his power.

Simon? - Otherwise ok but fails on power. 5 power is liability.
Sharon? - Not unless you need 3* filler. Sharon is OK, but not great and you are better off with Anki / Orenichi. For the budget Paolo is good enough.

For your budget

Orenichi, Aniki, Ace, Ivy, Paolo, Sharon, Murphy, Simon and your 3* choice (i would pick Veccio)

That is a very nice starting deck...in fact if you can't afford Sharon/Murphy you can just use whatever cards you currently have

When you finally make this deck concentrate on upgrading
Murphy> Desmond (only like 1k more)
Simon/Veccio>Milovan

Then you can gradually work towards Spiaghi/Oscar and Moses