2x is the dose - There are only two Ammo versions beyond that. Ammo itself comes in two scents, Standard and World Edition. Personally I’d suggest the World Edition scent is better for the more mature guy/woman. The pheros in both are the same, just select strength from the list box. At 48, I would second that you go for the 2x version from the start and I would have some 2x TUTH in reserve too.
Summer Ammo is the different version, with two extra molecules and probably the best scent of all but its a younger more chilled/laid-back product and maybe not what you are looking for just now?
How much is something you have to find for yourself as your effective dose is determined by your own body chemistry and situational factors unique to you, so a bit of testing different doses will be required.
Application points - Check the excellent sticky but don’t get too hung-up on them. If it has good circulation and is open to the air to diffuse, then its a viable point. Hiding pheros under clothes is for young guys, who need to tone-down sexual overtness. With you pushing 50 and her in her 30s, it will be the other way - you need to get all the pheros out there and she likely won’t be a shy flower when it comes to dose. However, some situations will call for more or less than others. Polite/daytime/work/hanging-out wil generally call for a less sexually overt dose compared to when you are out having fun, partying, clubbing etc. Then her feelings should be running higher and an over sexual will be much more tasty. 
Another couple of products you may want to consider are A314 and MX297.
A314 is a solid, mature status product that just screams quality and can be used to convey all the right LTR values and its effects linger, which helps withher “missing you” etc It can also be used with most of the pheros suggested already. IO and MX297 are the only ones to seriously avoid with it.
However, in some situations, MX297 can be a great friendzone-buster. If you go out, party and can throw yourself into it fully, then MX297/TUTH is great for the “I’ve not seen you this way before” moment but its not a combo I’d suggest for just hanging-out/talking. Use something different there.
Other products that may help steer the above primaries include:
P83 - Physical disinhibition.
IH/Instant Shine - Trust/bonding but steered in a playful/attractive direction.
P96 - Emotional comfort with arousal
TAC - Goofy/relaxing/adventurous. Typically after a night-out with an A314/TUTH mix, I’d bang-on 20-30mcg TAC and some more TUTH whenwe get home and get playful. 
You may also need to do more to demonstrate you mean business to her and to develop some more attractive personality traits/body language and very importantly step back from her to let her miss you a bit - sometimes this does a lot to help bring attraction to the fore. So don’t just tell her, pull right back and don’t be just her best friend. Let her chase you now. 