Well first off, join a club whether tri or bike, there will pretty much always be someone selling a bike but what is important is sizing and that is where having someone who knows what they are talking about helps.
I am a big fan of compacts; gearing-triple-double-or-compact-t47459-10.html#p56577
they are simply more flexible than a standard. Compact usually has a 50/34 set up, a Standard 53/39 but a compact can also have a 52 big ring and the inner a 36 or 39; Standard inner rings generally 42, 39 or perhaps 38 so you will struggle more on climbs. I tend to use a 52 or 50 - 39. Nice and tight, great for snicking through the gears and for something like the Vitruvian 50/36. IM UK 70.3 is hilly so a 50/36 or 50/34 would be useful.
Cassette, big fan of the SRAM 11-28; first 5 ratios the same as the 11-23 so again nice and tight and a big help with the 28 for climbing.
Fact: 50/11 is bigger, faster than a 53/12. What I mean there is if you can't maintain a useful cadence on 53/11 and have to drop to 53/12 you will get someone overtaking you on a 50/11 at the same cadence.
Wetsuits; most of us engage in varying degrees of drowning avoidance so look at something with good buoyancy around hips and lower limbs, 4-5 mm ideal, chest 3-5mm, arms 2- 2.5 mm . We tend to have bigger legs than swimmers so they tend to sink and cause drag, Blue Seventy Fusion is a good starter but I am not up to date on suits so unless anyone else can suggest something have a look at that - fit is King. Again you need someone who will not bull###t you and knows what they are talking about to size you. Now some wetsuit hire companies will let you buy the suit at a discount so that may be something to consider.
Hope that helps