You can buy a GRF-2N for around 6 million and then sell it after taking the DHS. That's the best source for DHS, I usually get my first 2N in the early-mid game.
Other good things to buy are particularly ERML++s, not only because they're good but also because if you're going to use them you'll probably want many of them, not just a couple per build. UAC2-5s I'd also buy a few of them, and other good buys are TTS+++, and RF+++. In fact unless we're talking about the Marauder (if you're interested in it) I'd always prioritize the weapons and equipment before the mech. An ANH can be very good, but only once it has good equipment and weapons. If not I'd rather take with me a much worse chassis but well equipped.
These are some examples of how gameplay preferences can mean so much.
1) I did get the Flashpoint SL Griffin, but if I found any more I'd add them to a lance rather than breaking them up for parts. I just added mine to a heavy lance because of its 204 alpha strike, and now I'm all atremble about the potential for losing it.
2) Love the ERMLs, but the only ones I've seen were on the Bull Shark, and that's my best mech, so they're not going anywhere.
3) I also love the computer game version of the ultras, and I've been swapping out ACs for ultras every chance I get. Finally being allowed to purchase from the Davion store has made a huge difference as they have an almost unlimited number of really great ultras, especially those that save tonnage. I was able to shoehorn an Ultra20 into a Rifleman, an Ultra10 into an Enforcer, Ultra5s all over the place, and by swapping out the two Ultra5s that came with the Bull Shark for lighter ones I was able to add an SRM4+++. In the early game, putting two Ultra2s in a Blackjack is very useful.
4) I've put RFs in 6 of my mechs, spread around to get one or two in each lance. I found a couple of ++++ in my 'save the princess' campaign, but nothing over +++ in Flashpoint so far. In the starter campaigns I've tried to split the head mods relatively equally between RFs and Comm systems, but in Flashpoint I've learned that there's a very good reason to keep the Cockpit Mods, so I'm now running about a third of each. I'm continually trying to train up new new pilots to replace losses, but random head hits, side torso losses and occasional falls seem to pile up on the guys I'm trying to get experience, which defeats the purpose. So, stick the trainees in the mechs with cockpit mods and they're much less likely to waste time in the infirmary.
5) On the other hand, I've found no use for TTSs. If they were weightless like Gyros and the head mods I'd be all over them, but at a ton per + there are just so many other things I'd prefer to spend weight on. Hitting things is rarely a problem in this game (unlike the board game where we always seem to be at 10 or higher for a target number).
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That brings up some odd pieces of equipment in the computer game.
First is the heat bank. After a lot of experimentation I've found a couple of mechs that get some utility from the banks, but really they're just a weird piece of equipment. What I do is divide the mech's 'excess heat value' into 100. (For example, my Phoenix Hawk has an EHV of 27, meaning if it jumps and fires an alpha strike it only sinks 33 of the nominal 60 heat it generates. 27 goes into 100 3.7 times. If I swap out the only optional heat sink for a 30 point heat bank the calculation becomes 30 EHV goes into 130 4.33 times, so making the swap makes some sense, if there are enough open critical slots (there are). The downside is that it takes longer to bleed heat the fewer heat sinks you have.
Which brings up the second odd piece of equipment — the gizmo (whose name I've forgotten) that reduces a percentage of weapon heat generated. To begin with, if you aren't generating 65 or more weapon heat you have no use for this, as you'll get at least as much benefit from heat sinks. (I suppose there could be some situations where there's only one open critical slot and jamming in a gizmo would be useful, but I haven't seen it.) If you're running double heat sinks you'd need to be generating at least 125 weapon heat to make them useful, and I don't think I've ever gotten over 100. If you're in the 65-84 heat range you'll save 7 or 8 heat with a 10% weapon reduction, which is a net -1 or -2 after taking out the equivalent weight in heat sinks. As a min/maxer I'd normally be all over that, but the same consideration arises as in the preceding paragraph, namely that the fewer heat sinks you carry the longer it takes to bleed heat once you get high, so you need to take that into account. For newbies, you'd need to be aware that these gizmos are multiplicative, not additive, which means that if you're generating 80 weapon heat and you add two -15% gizmos the weapon heat will reduce to 58 (80 x .85 x .85), not 56 (80 x .7). So, deciding which mechs would benefit from a gizmo is not always immediately obvious.
The third odd piece of equipment is the mortar. While I really enjoy the Bull Shark's reloadable two shot Thumper, a single-use Mortar just doesn't seem worthwhile to me, either in terms of weight, cost or critical spaces. And that's not taking into account how hard they are to find. Most stores don't sell them; when they do they'll only have 1 or 2 in stock; and they cost more than most light mechs. For a one-shot weapon, it's just not worth it. And I'm guessing you'd have to keep a mech in inventory that would spend most of its time in the racks, since running it short all those tons when you're out of mortar rounds would be silly.
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Looks like a gameplay preference thread would be more relevant.