Assalaamu alaykum. Does the name of Allaah "Al-Musawwir" mean that He can create totally unexisting new shapes? And does the name "Al-Waasi" mean that He has limitless capacity?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger. 

The name of Allah “Al-Musawwir” (The Bestower of forms/The Fashioner) entails what the questioner mentioned, that Allah is the One Who creates new shapes, though its meaning is more comprehensive, as was underlined by Al-Bayhaqi . He said in Al-Asmaa' wa As-Sifaat:

“Al-Haleemi said, 'It means the One Who creates forms and features of things with what He wills of similarities and differences. Recognition of creating new forms entails recognition of its accessories.' Al-Khattaabi said, 'Al-Musawwir is the One Who fashioned His creation in different images by means of which they can identify one another. Tasweer means planning and designing. Allah, The Exalted, created the human being in the mothers’ wombs in three distinct forms: first, a clinging clot (‘Alaqah); second, a lump of flesh (Mudhghah); and third, He gives it distinct features; Allah, The Exalted, says (what means): {So, blessed is Allah, the best of creators.} [Quran 23:14]’”

The well-versed scholar Haafith ibn Ahmad Al-Hakami said:

“Al-Musawwir means the Fashioner of the creatures with their distinguishing features and forms. It means that He causes whatever He wants to exist in the very form and features that He wills. It refers to giving each created thing its particular form. So, Allah, The Exalted, decrees what He creates, brings it into existence, and gives it its particular unique image. These are the three divine names in the concluding verse of Soorah Al-Hashr (chapter 59) {He is Allah, Al-Khaaliq (The Creator), Al-Baari’ (The Originator), Al-Musawwir (The Fashioner)...} [Quran 59:24]” [Ma‘aarij Al-Qabool]

Ibn Katheer commented on the verse, saying, “It means that when Allah wills something, He simply says, 'Be,' and it comes into existence in the form that He wills and the shape that He chooses. He says (what means): {In whatever form He willed has He assembled you.} [Quran 82:8].”

His name Al-Waasi’ comprises what the questioner mentioned, that there is no limit to His capacity, though its meaning is more comprehensive than this.

Al-Bayhaqi wrote, “Al-Haleemi said, 'It means that His Ability and Knowledge are extensive. It is an acknowledgment that Allah is able to do all things; nothing is difficult or impossible for Him, and nothing can be hidden from Him. His mercy encompasses all things. Abu Sulaymaan said, 'Al-Waasi’ is the One Whose richness encompasses all the aspects of poverty and need of His creation, and the sustenance that He bestows encompasses all His creation,'” [Al-Asmaa’ wa As-Sifaat]

The well-versed scholar As-Sa‘di wrote, “Al-Waasi’ means the One of broad extensive names and attributes and their accessories, such that none can praise Him fully; He is as He has praised Himself. He is of extensive grandeur, power, sovereignty, grace, and kindness.” [Tayseer Al-Kareem Ar-Rahmaan]

Allah knows best.