I started in a similar situation... I was 34, had no experience with airsoft, didn't know anybody who did, found out about it accidently and wish I had bought a different first gun.
IMO you should get an AEG rifle (like the M4) and make it your outdoor/milsim primary, while using the MP7 as your indoor/CQB primary and if you like as your outdoor/milsim secondary.
This is how I have organized my gear, my KWA MP7 (also my favourite gun) is mainly, but not exclusively, for CQB/indoor games.
Why? First the MP7 mags, like all other GBB mags, cost a fortune, but since I like picking my shots (as opposed to randomly firing away) I find that I don't go through too many bbs, so I do not need that many mags.
Second while it has decent range for outdoor CQB skirmish (I have been told) it cannot compete with rifles over long distances. So I keep it indoors, but I am thinking of using it as a secondary during outdoor milsims.
As long as your MP7 is at or below 350 fps you got a solid indoor/CQB weapon and besides mags you will not need anything else for it. Oh you should change the hop up unit on it but that's it for necessary upgrades as far as I am aware.
Now that you have your indoor gun you should IMO get and outdoor AEG rifle, like the G&P M4 (I have a CYMA AKM), wich can be used as your primary for outdoor/milsim games.
Why? First, it is an AEG and therefore the mags are not pricey and it can hold a lot of ammo (I like mid-caps and low caps, and dislike hi-caps). I have been told that during milsims I might be in situations where I have to defend against waves of attacks and having an AEG rifle makes sense because its mags hold more ammo and I can afford plenty of AEG mags.
Second, an AEG rifle has a longer range than the MP7 and that is handy when outdoors.
Having a indoor/CQB gun and a different outdoor/milsim gun is just my opinion and there lots of people on these forums that are much more knowledgeable than I am regarding airsoft.
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