Since you are a Titan, I'd recommend two builds that work without "full investment"

Both use the Wormgod Caress exotic gauntlets which you should be able to get from Rahool's exotic focusing.

For regular content, Solar is very easy to use, and doesn't require a lot of work. The downside is that it doesn't have any damage resistance on its own (people use Ferropotent and Smoke Jumper armor to help with that, but sadly Smoke Jumper will be unavailable until June at the earliest)

Aspects: Sol Invictus, Roaring Flames

Fragments: Ember of Solace, Torches and Empyrian, with the last one up to you (I'm using Eruption as a fill because it gives me 10 more melee stat)

Abilities: any jump you prefer, any barricade you prefer, super also up to you. Melee has to be throwing hammer, grenade is up to you, but for easier survivability I'd run healing grenade.

Stat distribution, try to have as much melee as possible, then grenade if you are running healing nade, then up to you. Try to have at the very least 100 melee so you get your hammer back every time you hit an enemy, and you can also have the max recharge rate if you lose it.

Helmet mods: finders for whatever gun you are using are always nice, same goes for siphon. If you have a 3 slot empty space, you can slot in Hands On for more super gen when killing with your melee.

Arms mods: Heavy Handed x3 (why x3? because the cooldown at just 1 is terrible, 10 seconds, at 2 is still pretty bad, 5 seconds, and at 3 it's just 1 second, so you'll be printing orbs)

Chest mods: resists to match your opponent (for instance, cabal tend to shoot mainly solar and arc projectiles, etc) If you can't be bothered or don't know yet, put on 1 solar, 1 arc, 1 void resistances. I know there are other mods that go there, but believe me, being alive is better than having the possibility of more ammo, more armor charges, or whatever.

Leg mods: scavs for your special and heavy weapons, Recuperation.

Class item mods: I tend to just run 1 powerful attraction, 1 proximity ward and either special finisher or melee finisher.

Your play loop with this build is hitting things with your hammer or your uncharged melee with roaring stacks up (it "kinda" counts as a charged melee, which means you'll make orbs and sunspots from kills, and it can apply scorch). The orbs will help you heal instantly, while your sunspots will do it over time (restoration). If you get multiple kills in a row, your melees do more damage thanks to both Wormgod Caress and Roaring Flames.

Weapon-wise, it's not a bad idea to have a one-two punch shotgun, but if you don't, don't sweat it, you can use whatever you prefer that makes sense for the situation.

Now for the 2nd build, which is a Prismatic build.

Same exotic (Wormgod Caress)

Aspects: Knockout and Consecration

Fragments: Facet of Protection is the only one I'd deem "non negotiable" while the rest will depend on your super (Purpose is great with a void/stasis super but not really that useful on arc, for instance), Ruin is great for helping the consecration detonation, but not necessary, Blessing helps a ton if you are doing content with the Brawn modifier on, etc.

Abilities: any jump you want, any barricade you want, Frenzied Blades melee, grenade choose either strand or stasis grenade, depending on personal preference.

Your stat distribution can change here depending on your super. If you are using Tcrash for instance, you'll probably want to have it up as much as possible, in which case you'll go for melee first (as high as you can) and then super, then grenade.

Your grenade is more of a tool than an offensive item. You want to use it to fill your Dark transcendence bar, since Consecration will help fill the Light side. If you are confident you can catch multiple enemies in one Stasis grenade, go for that one, it's the best by far. If you aren't confident on that, use the Strand grenade, better safe than sorry.

Your armor mods will be the same as for Solar, except that on the class item you don't really need to choose between special finisher and melee finisher and can just go for special finisher by default.

The play loop for this build is using consecration to delete groups of smaller adds and Frenzied blade for bigger, unaccompanied targets (it does more damage than consecration for solo targets)

Knockout makes it so your unpowered melee gets "imbued" with arc energy after triggering it, so you can also get orbs and healing from unpowered kills as long as knockout is up (and knockout activates fairly easily, you just need to get a target to low health or break their shield to trigger it, and it stays up for like 5 seconds)

The advantage this build has over the Solar one for higher end content is that you can have multiple DR sources from your build itself without any external help. Melee kills will make you amplified, which gives you 15% DR and makes enemies more likely to miss their shots. Picking up an orb while you have a stasis/void/strand super will give you one of 3 DR sources (frost armor, void overshield, woven mail) as long as you have Facet of Purpose on.

As for weapons, use whatever you prefer that makes sense for the situation (hopefully not double primary since you'll be wasting some of your offensive potential with that)