Chapter 1 - Space Marines
There are really two ways of representing Space Marines in games set in the 40k universe.
One is the "balanced" way where Space Marines are more in line with other denizens of the setting, either because you want to incorporate them easier into parties composed largely of other humans, or because you emphasize the "enemies'" point of view where Space Marines are supposed to bow down to the superior might of non-human beings. An extreme example is the Fire Warrior video game, where a single Tau Fire Warrior managed to slaughter something like a company of Space Marines and IIRC a Dreadnought all by himself.
The other is the "fluffy" way, where Space Marines can eat, literally (cf. Omophagea implant), just about anything and everything. Now the "fluff" itself is an extremely problematic issue with 40k, having been subjected to countless retcons and direction changes, not even getting into the mess that is Black Library novels*. But in almost all occasions Space Marines are represented as quite literally superhuman.
I'll let it be known that I
love Space Marines. Not because of the wish fulfillment angle - on the contrary, I find it very difficult to personally identify with one. But they really personify the Warhammer 40,000 universe to me by representing the same path Mankind have gone in the far future - sacrificing a lot of their humanity to at least have a small hope of overcoming the odds that would look impossible for us here today.
(As you can see, I find Mankind and the Imperium very fascinating and thought-provoking on a philosophical level, but I'll leave that for later. Sadly, this hasn't been explored much in the recent years, being abandoned in favor of the TOTALMETALWAR stuff, which, while fine by itself, is a different thing altogether.)
So there's no doubt that I went the second route, making Space Marines as powerful in comparison to normal, "real" people as appropriate to the Imperial accounts. That means they're not nearly close in their combat capabilities to a usual first level Soldier (especially as I prefer to use the BO option of buying Talents and not Talent Points) - and that's how it should be!
markc, I wanted to say the same thing that you did
Space Marines aren't really first level characters. I feel that a Space Marine would get promoted from Scout to a full fledged Marine somewhere around level 4 to 7, then to a Veteran somewhere around 12 to 15 and the highest ranking Chapter officials should usually be somewhere between 20 and 30, with Mephiston the Lord of Death, the most powerful Marine Librarian in the 41st millenium, scraping the 50. In comparison, Grey Knights probably only embark on active duty by level 10 to 12, Grey Knight Terminators and Adeptus Custodes are above level 20
each, with their officals somewhere above 30 at least. Primarchs were in the Silmarillion levels of Elven lords of old with the Emperor and the Ruinous Powers somewhere on par with Valar.
In the grim darkness of the 41st Millenium there is only war. And Space Marines get a lot of practice.
Not that it's impossible to roleplay a Space Marine in their training. Far from it - in my opinion that would be an extremely interesting roleplaying experience.
In that case you should split the starting list of talents into several parts (remember that the implants are introduced in the order listed) and give part of the benefits to PCs each level until they're fully grown, matured and ready to kick (even more) ass.
That's actually how I tried to implement the implants in one of the older versions of this system, before I settled on the present one. The character gets a (relatively modest) set of starting talents and then gains levels, while also paying EP cost for the implants gained (1 TP = 1,000 EP). A fully developed level 7 Space Marine would thus need as many EPs as a different character for advancing to level 13.
The talent list isn't exactly the same as with the new one, by the way. Since you won't use both systems in the same game it's not that bad, though I should probably try and bring it up to date with the new version.
You can see the old system (as well as a couple of really old ones)
here.
[insert stuff I forgot about but will hopefully remember and add]
*The authors who can write reasonably well often don't have the best idea of the setting (Abnett, though he got better during the years - or at least subjected to better quality control), those who do aren't much of writers (Graham McNeil), some just flat out suck (CS Goto) and people who have both (Ian Watson) don't work there anymore. Therefore Black Library novels are explicitly non-canon in my games, unless individually approved.
Upcoming: A weapon cannot substitute for zeal.