I don't think modding and carrying 4 or 5 guns are alternatives, nor mutually exclusive, nor individually routes to building an effective loadout even if your preferred tactics favor either of those actions.
Personally, I would keep it simple and clean. My two cents are that at most, you should run a primary, secondary and backup. For me, that is Swarmpede/NSE Vulcan/Rayven, optional Swarmpistol and Jolt/socks.
I would only advocate adding any weapons to that if (1) you just can't reload or clear malfunctions under pressure and prefer a New York Reload instead, or (2) you are what the "TF2 HVZ classes" types call a grenadier, i.e. you have an absolved airgun, rocket launcher, sock cannon or other special weapons.
If you just want to be an effective human...
1. Build that stampede. Make it reliable. You need to be able to trust your life to it, remember. I would just go for the proven SGnerf spring, and 12 cells Ni-cd/Ni-MH (RC packs). That will get you squarely in the "both ROF and range" quadrant but the spring isn't just stupid overkill when applied to streamlines (like my everbilt is...) and the cyclic rate is easily handled by most guns without much tuning to get them stable. Many push trustfire, and other 14500/18650 cells with holders but these are not the most reliable nor the safest nor the highest performance option. Packs are all 3 at once. Avoid tamiya connectors due to unreliability; I use Deans but there are a lot of options out there that will do it.
2. Obtain as many stampede mags as you could possibly need (rule of thumb is to treat this like a firearm, ammo is NOT reusable and if you fire a round it is gone!) to get through a tight situation.
3. Buy decent ammo. Read the dart code thread, and choose streamlines wisely - or if NSE darts are available, use these. Test before stocking up; some guns don't like certain types. My swarmpede chokes quite predictably on T-codes unless I have CA coated the tips to kill friction. Keep game ammo separate from training rounds, and keep it in mint condition until you actually need it.
4. Practice handling and shooting. You should be able to do mag changes in under a second, clear malfunctions in your sleep, and wish you were holding your stampede every time you are away from it. "This is my rifle. There are many like it, but this one..." You get the picture.
Socks seem to be getting some attention, so I will just say that they are specialized. If you can use them effectively, great - but they are not universal. Fair warning. I am hardwired for guns and older defensive tactics, and just can't skirmish, or do much of any damage with socks.
One of the big barriers for me is ammunition. I'd like to pick up a Spectre, and I can get one locally for around $17, but it doesn't fire streamlines/elites which my Stampede and most of my team-mates will be using. Using a Recon as a pistol is attractive, but I'm not going to be able to get one for under $30. With basic mods my Stampede will be running me about $90-$100 and then I need accessories and ammunition, probably about another $100. That's about my budget, I think...
No reason a spectre can't shoot streamlines. Delete pegs, isn't that SOP by now? Elite, do not interfere with pegs anyway, shorter core. I also assume you meant NSE Retaliator, not Recon which is obsolete, saddled with a handful of longstanding problems and worth about $10 used and falling. I have to agree, retaliator is an awesome platform but if you only need a sidearm I would spend the $30 on a swarmfire, and make yourself a swarmpistol - or if no-modding-required factor is desired and you are OK with spendy, flaky, obsolete guns, go RF20. A good subgun is the best insurance policy you can have in this game.