Like mirko said - for me antivirus is useless. When u're downloading sth u must use your brain to find out what is happening. Simply example - some kind of exploit from steam. Guy sending u a link to download a screenshoot showing some stuff from cs:go. U downloading it and open that file. Problem is, that u diidn't check a enlargement (because meybe u didin't think about checking that or u didin't have selected option to showing that all time). Ofc file opened paint, but because that was an exe file - it added to tasks. What this exploit was doing ? Sending messages to probably all friends from steam with that link. Ofc it's not a virus, simply exploit and it won't doing sth worse (like trojans or sth like that - btw. trojans - simply way to try ddos some1 from acquired computers), but it was a simply expamle how u can simply be fucked up because of yours "stupidity". But I think one thing can help u with dat: sth like System monitor (from for example Rainmeter - image will be send in this post). You can replace your antivirus by Rainmeter with Illustro skin (rainmeter takes 1-2% from cpu and has got about 14 mb with these all overlays on ss). Really useful thing.
With ssd discs there is one problem - price. 1TB good hdd (like wd blue disc) - about 40 euro. SSD disc 128gb (like intel 540) - about 50 euro. Desktop computers - simply u just buying sata cable, connecting that and wuala - u don't want to worry about space - most cases have got many space for 3,5 cal discs. Some cases has got ofc space for 2,5 cal discs, but also u can easily ount ssd in 3,5 bay because of adapter from 3,5 to 2,5 But laptop ..... It's laptop. Most laptops have got only one slot for disc. Ofc, u can buy ssd disc with more than 128 gb space, but .... money
P.S Sorry for long post - i can talk about computers hours or write poems about dat
P.P.S And sorry for any mistakes - I was writing fast, so some sentences can not be logical etc. Sorry once again for that.