Hello,

I'm currently using CRS112-8P-4S model but it can't handle the rouing, firewall,vpn etc. and overloads the CPU. What is the cheapest alternative for it to suggest me that can handle the jobs.
Thanks in advance.

What are requirements? Most importantly, what are throughputs required (both WAN with heavy firewalling and LAN-to-LAN with limited firewalling)?

2 wan 100 mbps 1 lan mangle rules for routing, ddos protection filter rules, l2tp or sstp vpn, some nat rules for security devices and servers and maybe VLAN.

If you'll search yourself: every Mikrotik device has test results published. This is data for CRS112. Many people on this forum find figure under "Ethernet test results -> Routing -> 25 ip filter rules" column "512 byte" (for your device that's 32.8 Mbps) to tepresent real-life performance quite well. Of course it very much depends on actual configuration, my estimation is that your requirements might be on the heavy side and actual throughput limit might be even slightly lower than this figure.

You need device which will be capable of routing of at least 300Mbps (plus) routing capacity, possibly quite higher due to tunnels you want to run (encryption might not be HW offloaded depending on device model, tunnel type and encryption parameters and that will severely limit performance of tunnels).
My suggestion would be either RB5009 or RB4011 (the former being newer model and generally a bit nicer device). If you're on tight budget, have a look at some of wireless devices such as hAP ax2 or hAP ax3, they have pretty decent CPU ... and you can always turn off wireless if it would bother you.

Okey i will check them. Thank you.