The reason people suggest avoiding -ghach is to avoid the trap that you just fell into: adding a suffix (usually -taH) just because you're supposed to, but not really meaning that suffix.

vuttaHghach doesn't mean cooking, it means an ongoing act of cooking, or continuous cooking. That's not what you mean when you want to say I like to cook. What you'd want to say is *vutghach vIparHa', but you can't say that.

Make no mistake: adding -ghach to a bare verb is wrong, even though Okrand simply called it "marked." Okrand tells us in HolQeD 3:3 that saying *belghach is like saying *pleasureness. We all understand it, but you don't say it. Klingons might not take it as badly as we would take *pleasureness, but it's still not right.

The idea behind -ghach is this. Imagine you've got a verb like bel, and you've got a magic nominalizer button that, when pressed, turns the verb bel into the noun bel. Imagine this button works on any verb, but for the moment forget about verbs that don't have known noun counterparts (like tlhutlh). Stick a suffix on the verb, and press the button. When we put, say, -taH onto bel to get beltaH be continuously pleased and then press the button, nothing happens. The presence of the suffix blocks our nominalization button. So Okrand comes along and gives us a magic suffix, -ghach, which when stuck on the end counteracts the presence of the blocking suffix and lets the nominalizer button work again. We add the suffix and push the button and ZAP! we get beltaHghach ongoing pleasure.

The point of -ghach is to hide the verb's other suffixes from the nominalization process, so you can turn the suffixed verb into a noun again.

Now, the funny thing is, this process works to counteract suffixes and nominalize verbs that don't actually have noun counterparts! So while I can't use tlhutlh to mean a drink, I CAN say tlhutlhtaHghach ongoing drinking.

So people find themselves wanting to use -ghach on verbs that don't have noun counterparts, but they're not actually interested in counteracting suffixes; they just want a noun form of the verb. But, the rules say, you can't really use -ghach without a suffix. So they go and pick the one that least changes the meaning of the verb (usually -taH) just so they can get access to -ghach, even though they're not using it for its real purpose.

TL;DR: WHENEVER YOU FEEL AN URGE TO USE -ghach ON A BARE VERB, DON'T USE -ghach AT ALL. Find some other way to say what you want to say, like sentences-as-objects.

And no, don't put prefixes on verbs with -ghach. We don't think you're supposed to do that.