Hey, so I'm researching the Esperanto aspects, and I'm trying to work out exactly how many there are. Most of them are quite well attested, but others seem less so, so I was hoping that someone with more experience than myself could check and see if I've got them right. What I've got so far:

• Perfect, progressive & prospective aspect are expressed as compound tenses via esti + the past, present or future participles respectively (these constructions can also be contracted to form synthetic forms by removing esti all together and replacing the participle's adjectival ending with an ending of tense), for example: mi estas kaptinta or mi kaptintas (I have caught; present perfect); mi estis kaptinta or mi kaptintis (I had caught; past perfect).
  
• The perfective (inceptive) aspect is expressed via the prefix "ek-" e.g. I began learning Esperanto ---> mi eklernis Esperanton
  
• A generic imperfective expressed -ad-, which is inserted between the verb's stem & it's ending (-i for infinitive)
  
• The effective aspect, which signals actions completed to a significant degree (not dissimilar to telicity as an aspect, as I understand it), is expressed via the prefix el- (repurposing the preposition el, meaning "from" )

Also, what is the exact meaning of the -ad- aspect? I understand it is imperfective, but how exactly? Does it refer to habitual actions (and by extension could it be used to translate constructions like English used to for the habitual past)?

PIV; about -ad: Verbojn el morfemoj signifantaj agon aŭ objekton, por prezenti la agon en ĝia malvolviĝo k insisti pri ĝia daŭro aŭ ripetiĝo: marteladi (longe m.); vizitadi (ofte aŭ regule viziti); mi saltadis la tutan tagon de loko al loko; Karolino ĉiam obeadis la ordonojn de sia patrino, sed hodiaŭ ŝi ne obeis; kiam mi venis al li, li finadis sian laboron; dum en unu ĉambro la gastoj dancadis, en la dua ĉambro estis preparata la vespermanĝo. Rim. 4 Kiel videble el la tri lastaj ekz-oj tiu ĉi formo similas la imperfekton de la latinidaj lingvoj.

Yes, it can be used like English used to with -is ending. It can also be used like English Present Simple.

Article about aspects and telicity

The meaning of 'used to' in English is that one did, but at some point one ceased to do.

That you may be actually be doing it again now, does not actually prevent the use of 'used to', though often it will be the case that you no longer do it.

Thus some one who in adult life purchases their erstwhile childhood home, can still say I used to live here as a child.

This is not the meaning of -adis, which emphasizes repetition or has a durative aspect.

I used to can be translated into Esperanto by Mi (t)iam -is, with its implication that at some point you stopped.

Mi iam estis studento de Profesoro Jones - I used to be a student of Professor Jones

But often the simple past will suffice as the context will provide the clue that whatever went on in the past ceased at some point.

Eg Kiam infano, mi kredis ke .. - As a child, I used to think that ....