u/Financial-Plum-4535

Hi folks,
today I finished my first tapestry crochet and I have a few question regarding the blocking process.
I am a full blood amigurumi crochet person so I have no prior experience with blocking.
So my questions:

1. I used chenille yarn. On other posts I read that blocking chenille yarn doesnt do much so most people just leave it. Is that so? Should you still pin it down so it streches?
2. I will start using thinner yarn and then I surely need to block it. Are there any cheap options? I dont have an Iron so I will not be able to steam it and to pin it down I sah a few streachingboards (dont know if that is correct, I am german and dont know the english word haha) they were quite expensive vor 1m x 1m. So my thought was coudln't I juse just foam playmatts for kids you know like the puzzle ones that are like 2 cm thick or is there an even cheaper substitude? I really would appreciate some cheap solutions.
3. Not a blocking question but a tapestry question. With using chenille yarn in some places the yarn I used the row beforehand shone through the upper row, is that because some tension was too loose? Too firm? Or does the size of the hook has an impact on that? On the yarn it said 7mm hook but as experienced amigurumi person I always size down so I used a 5mm

Would really appreciate some answers, love goes out to yall <3 Have a great day!