Dear Frank,
It is very difficult to pronounce 'ca' by a western tongue, unless it is through 'listening' and copying. Do not try to find those sounds in your own language. A westerner would normally pronounce both canda and chanda as chaandaa, with long vowels. The other areas of difficulty are unaspirated letters, dentals and linguals, and adjunct consonants. Therefore, kamma becomes 'khaamaa' Dhamma becomes '.Dhaamaa', 'piti' becomes 'phi.ti'. The short vowel 'a' becomes 'aa'.

You are right about puffing out the air. The best way to practice, if there is no one to give you 'sound' to copy is by placing your hand in front of your mouth while you pronounce. You should feel more gusts striking your hand than when you pronounce aspirate consonants.

As for 'dvi',the pronunciation is somehow: dwi. Pronounce 'dw' like in 'dwarf'. When you pronounce it, make sure your front part of the tongue, not just the tip, strikes the root of your upper teeth. It is a dental unaspirate. Therefore, see that you do not to pronounce it '.dwi'.

When you pronounce words like 'bhikkhu', if you put stress in the vowel just before conjunct consonant, here 'i', it will be easily pronounced. Grammatically, it is called garuu (Padaruupasiddhi 6). When you have to pronounce this type of word, you should consider the nature of pali alphabets. Pali consonants cannot be pronounced without help of a vowel. So, that vowel should either be in front of that consonant, or at the back. For example, In 'chanda' 'ch' will depend on following 'a', 'n' will depend on preceding 'a', and 'd' will depend on final 'a'. The '.m' always depends on proceeding vowel.

When it comes to pronouncing double consonants, the first consonant that is without vowel depends on the vowel that precedes it. So 'ik'. Then add 'khu'. Try pronouncing 'ik-khu' 'ik-khu'for some time and then add 'bh' at the beginning. It should be o.k. Take note that 'k' in 'ik' is not aspirate.

Good Luck and Be Happy
Bhante Sobhana

N.B. In pali language, it is important to practice than to pronounce. You may pronounce karu.naa as khaarunaa, but if you are compassionate, nobody pronounced better than you.